diff --git a/install.ps1 b/install.ps1
index 37ec12874..db72b7c21 100644
--- a/install.ps1
+++ b/install.ps1
@@ -16,7 +16,7 @@
     # and Invoke-WebRequest throws on a cut transfer before the hash is read:
     # the site's build rewrites this line there (scripts/sitebootstrap.py).
     $mismatchAdvice = "The download was most likely cut short: try again. Within minutes of an update of this project the two files can come from caches of different ages. Waiting five minutes settles that."
-    $defaultInstallSha256 = "86f11e91316119889fda8a2baa228a9b7be1c1d3fd29780473a59e412e362c7d"
+    $defaultInstallSha256 = "403b6e8a7efcd24858b0f46ffa19c2b9012cdeef149768729d8e48d0b68a296a"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }
diff --git a/install.py b/install.py
index e81a361ed..c9894999b 100644
--- a/install.py
+++ b/install.py
@@ -8481,7 +8481,10 @@ def _print_menu_head(
         named = ", " + ", ".join(filter(None, [
             f"for {held} of {total} systems" + (" (--system)" if flag else "")
             if systems else "",
-            ("--core" if flag else f"{_plural(len(cores), 'core')} chosen") if cores else "",
+            # Out of the cores the systems chosen offered, as Cores counts
+            # them: "1 core chosen" read as one of one.
+            ("--core" if flag else cores_words(len(cores), len(available_choices(
+                *narrow(files, omitted, systems, [], []))["cores"]))) if cores else "",
             ("--region" if flag else "regions ranked") if regions else ""]))
         named = "" if named == ", " else named
     if current is not given:
@@ -8665,7 +8668,10 @@ def _choose_narrowing(files: list[dict], omitted: list[dict], manifest: dict | N
     core_names = available_choices(kept, kept_omitted)["cores"]
     if len(core_names) > 1:
         print("\nThe platform's own files for these systems are always kept.")
-        print("The extra files each core loads can be narrowed.")
+        # Every core is kept, as Cores draws them all ticked: a list of
+        # numbers read as nothing chosen yet.
+        print("Every core's extra files are kept: Enter keeps them all, numbers keep "
+              "only those cores.")
         cores = _pick("Cores:", [
             (core, _filter_by_target(
                 [f for f in kept if f.get("cores") is not None], [core]))
@@ -14620,6 +14626,11 @@ class TuiState:
         self.region_order: list[str] = []
         # The cores of every system listed, after "Cores of the other systems".
         self.cores_all: bool = False
+        # None pressed on Cores: no core ticked, which no option says
+        # (state.cores empty is every core). Done is refused until one is.
+        self.no_cores: bool = False
+        # The cores --core named, as line mode names them on its head.
+        self.cli_cores: list = []
         # The names of the systems ticked before a check counted again, and
         # those of them that hold nothing under its options.
         self.ticked_names: dict[str, str] = {}
@@ -15364,6 +15375,26 @@ def tui_choices(state: TuiState) -> dict[str, list[str]]:
     return available_choices(manifest.get("files", []), manifest.get("omitted_files", []))
 
 
+def core_ticked(state: TuiState, name: str) -> bool:
+    """Whether Cores draws name ticked: every core while none narrows the
+    run (state.cores empty), else those chosen."""
+    return name in state.cores or (not state.cores and not state.no_cores)
+
+
+def _core_base(state: TuiState) -> list[str]:
+    """The cores a choice on Cores is made among: those of the systems
+    chosen, every core of the list else."""
+    every = tui_choices(state)["cores"]
+    theirs = _chosen_cores(state)
+    return every if theirs is None else [name for name in every if name in theirs]
+
+
+def cores_words(chosen: int, total: int) -> str:
+    """The cores a run keeps, as the plan, Options and line mode say it:
+    all cores, or 3 of 12 cores."""
+    return "all cores" if not chosen or chosen >= total else f"{chosen} of {total} cores"
+
+
 def _chosen_cores(state: TuiState) -> set[str] | None:
     """The cores the files of the systems chosen name, None when every
     system is chosen."""
@@ -15492,8 +15523,11 @@ def tui_rows(state: TuiState) -> list[TuiRow]:
         # stays in view.
         shown = every if theirs is None or state.cores_all else [
             name for name in every if name in theirs or name in state.cores]
-        rows = [_filter_row(state)] + [
-            TuiRow("core", f"[{'x' if name in state.cores else ' '}] {name}", value=name)
+        # Every core ticked when no core narrows the run, as Choose systems
+        # ticks every system: all boxes empty read as nothing chosen, and
+        # the owner ticked each one by hand.
+        rows = [TuiRow("all", "All"), TuiRow("none", "None"), _filter_row(state)] + [
+            TuiRow("core", f"[{'x' if core_ticked(state, name) else ' '}] {name}", value=name)
             for name in shown if _matches(name, needle)]
         hidden = len(every) - len(shown)
         if hidden:
@@ -15818,8 +15852,9 @@ def _option_rows(state: TuiState) -> list[TuiRow]:
                            f"{_yes(state.installed_only)} ({found} found)",
                            "--installed-cores"))
     if choices["cores"]:
-        chosen = f"{len(state.cores)} chosen" if state.cores else "all"
-        rows.append(TuiRow("cores", f"Cores: {chosen}", "--core"))
+        # The plan's words, the noun left to the row's own label.
+        rows.append(TuiRow("cores", "Cores: " + cores_words(
+            len(state.cores), len(_core_base(state))).replace(" cores", ""), "--core"))
     copied = ", ".join(str(folder) for folder in state.from_folders) or "none"
     if manifest.get("save_directory"):
         # The interface said "Name it with --save-dir" and had no row for it.
@@ -15908,6 +15943,9 @@ def _back(state: TuiState) -> list[tuple]:
             chose = False
     if state.screen == "regions":
         state.region_order = []
+    if state.screen == "cores" and state.no_cores:
+        # None, then Esc: no core ticked is no choice, and every core is kept.
+        state.no_cores = False
     state.stack.pop()
     if chose and state.screen == "plan":
         # The systems chosen, the next press is Install: Back left the focus
@@ -16665,6 +16703,18 @@ def _activate(state: TuiState, row: TuiRow) -> list[tuple]:
         if action == "morecores":
             state.cores_all = True
             return []
+        if action == "all":
+            state.cores, state.no_cores = [], False
+            return []
+        if action == "none":
+            state.cores, state.no_cores = [], True
+            state.focus["cores"] = next(
+                (i for i, item in enumerate(tui_rows(state)) if item.action == "core"),
+                state.focus.get("cores", 0))
+            return []
+        if state.no_cores:
+            state.status = "No core is ticked: tick one, or choose All."
+            return []
         return _back(state)
     if screen == "confirm":
         if action == "install":
@@ -17148,7 +17198,7 @@ def _option(state: TuiState, action: str, step: int) -> list[tuple]:
     elif action == "cores":
         # On the first core: the filter row under A opened a field a
         # controller cannot type into.
-        return _push(state, action, 1 if tui_choices(state)["cores"] else 0)
+        return _push(state, action, 3 if tui_choices(state)["cores"] else 2)
     elif action == "regions":
         state.region_order = []
         _push(state, action)
@@ -17252,7 +17302,7 @@ def _tick(state: TuiState, row: TuiRow, on: bool | None) -> None:
     if state.screen == "systems" and row.action == "system":
         chosen = state.ticked
     elif state.screen == "cores" and row.action == "core":
-        chosen = set(state.cores)
+        chosen = {name for name in tui_choices(state)["cores"] if core_ticked(state, name)}
     else:
         return
     value = row.value
@@ -17262,10 +17312,20 @@ def _tick(state: TuiState, row: TuiRow, on: bool | None) -> None:
             state.ticked.add(value)
         else:
             state.ticked.discard(value)
-    elif want and value not in state.cores:
-        state.cores.append(value)
-    elif not want and value in state.cores:
+    elif want:
+        if value not in state.cores:
+            state.cores.append(value)
+        state.no_cores = False
+        if set(_core_base(state)) <= set(state.cores):
+            # Every core ticked again: no narrowing, as before.
+            state.cores = []
+    elif not state.cores and not state.no_cores:
+        # Every core was ticked: one untick keeps the others.
+        state.cores = [name for name in _core_base(state) if name != value]
+        state.no_cores = not state.cores
+    elif value in state.cores:
         state.cores.remove(value)
+        state.no_cores = not state.cores
 
 
 def _edit_text(text: str, key: TuiKey, selected: bool = False) -> str | None:
@@ -18965,7 +19025,12 @@ def _view_plan(state: TuiState, width: int, height: int) -> tuple:
         at += 1
     named = [*([f"for {len(state.systems)} of {len(tui_systems(state))} systems (--system)"]
                 if state.cli_systems and state.systems else []),
-             *(["--core"] if state.cores else []), *(["--region"] if state.regions else [])]
+             # Named on the command line as line mode names it, chosen on
+             # Cores out of how many: "--core" said nothing of the count.
+             *([("--core" if state.cores == state.cli_cores else
+                 cores_words(len(state.cores), len(_core_base(state))))]
+               if state.cores else []),
+             *(["--region"] if state.regions else [])]
     said = ", ".join(named)
     # A system --system named that --no-game-data left empty, in line mode's
     # words (tui_audit_16 P3-7).
@@ -19241,16 +19306,21 @@ def _middle_label(row: TuiRow, room: int) -> TuiRow:
 
 
 def _view_regions(state: TuiState, width: int, height: int) -> tuple:
+    # An order, not a set: ticked all, it would rank regions nobody ranked.
+    # None ticked keeps every region, said so.
     before = ["Tick the regions to keep, best first. Where a system has one BIOS "
-              "per region, the best one found is installed."]
+              "per region, the best one found is installed. With none ticked, every "
+              "region's BIOS is kept."]
     return ("Preferred regions",
             _compose(state, width, height, before, tui_rows(state)),
             ("A/Enter Tick", "B/Esc Done", "Left/Right Order", "? Help"))
 
 
 def _view_cores(state: TuiState, width: int, height: int) -> tuple:
-    before = ["Tick the cores you use. With none ticked, every core's files are kept."]
-    return ("Cores", _compose(state, width, height, before, tui_rows(state)),
+    before = ["Every core ticked keeps every core's files. Untick the cores you do not "
+              "use: the platform's own files are always kept."]
+    status = [state.status] if state.status else []
+    return ("Cores", _compose(state, width, height, before, tui_rows(state), status),
             ("A/Enter Done", "B/Esc Back", "X/Space Tick", "? Help"))
 
 
@@ -20233,6 +20303,7 @@ def tui_start(
     state.cores = list(dict.fromkeys(
         token.strip() for value in args.core or [] for token in value.split(",")
         if token.strip()))
+    state.cli_cores = list(state.cores)
     state.no_game_data = state.cli_no_game_data = bool(args.no_game_data)
     state.installed_only = bool(args.installed_cores)
     state.jobs = args.jobs
diff --git a/install.sh b/install.sh
index 26f947c7e..cacf12717 100755
--- a/install.sh
+++ b/install.sh
@@ -23,7 +23,7 @@ DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/ins
 # curl or wget stop on a cut transfer before the hash is read: the site's
 # build rewrites this line there (scripts/sitebootstrap.py).
 MISMATCH_ADVICE="The download was most likely cut short: try again. Within minutes of an update of this project the two files can come from caches of different ages. Waiting five minutes settles that."
-DEFAULT_INSTALL_SHA256="86f11e91316119889fda8a2baa228a9b7be1c1d3fd29780473a59e412e362c7d"
+DEFAULT_INSTALL_SHA256="403b6e8a7efcd24858b0f46ffa19c2b9012cdeef149768729d8e48d0b68a296a"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {
diff --git a/install/launchers/index.json b/install/launchers/index.json
index bd040ac20..19f5a91c4 100644
--- a/install/launchers/index.json
+++ b/install/launchers/index.json
@@ -27,8 +27,8 @@
         {
           "dest": "roms/ports/retrobios/install.py",
           "repo_path": "install.py",
-          "size": 981280,
-          "sha256": "86f11e91316119889fda8a2baa228a9b7be1c1d3fd29780473a59e412e362c7d",
+          "size": 984900,
+          "sha256": "403b6e8a7efcd24858b0f46ffa19c2b9012cdeef149768729d8e48d0b68a296a",
           "executable": false
         },
         {
@@ -71,8 +71,8 @@
     "muos": {
       "archive": {
         "dest": "ARCHIVE/RetroBIOS.muxapp",
-        "size": 1034457,
-        "sha256": "92d78b81459583ea9ac00546e28f3118e815ac302c0f180e882b44a16e5bcb53"
+        "size": 1038077,
+        "sha256": "49b9de6afa23afda4f6c786fa0968c36af1bd2ec9b52cb0927df4c527dcc701c"
       },
       "members": [
         {
@@ -92,8 +92,8 @@
         {
           "name": "RetroBIOS/install.py",
           "repo_path": "install.py",
-          "size": 981280,
-          "sha256": "86f11e91316119889fda8a2baa228a9b7be1c1d3fd29780473a59e412e362c7d",
+          "size": 984900,
+          "sha256": "403b6e8a7efcd24858b0f46ffa19c2b9012cdeef149768729d8e48d0b68a296a",
           "executable": false
         },
         {
@@ -166,8 +166,8 @@
         {
           "dest": ".config/modules/retrobios/install.py",
           "repo_path": "install.py",
-          "size": 981280,
-          "sha256": "86f11e91316119889fda8a2baa228a9b7be1c1d3fd29780473a59e412e362c7d",
+          "size": 984900,
+          "sha256": "403b6e8a7efcd24858b0f46ffa19c2b9012cdeef149768729d8e48d0b68a296a",
           "executable": false
         },
         {
diff --git a/tests/fixtures/tui/colour-120x40.txt b/tests/fixtures/tui/colour-120x40.txt
index 376973b2e..7b7a0d47d 100644
--- a/tests/fixtures/tui/colour-120x40.txt
+++ b/tests/fixtures/tui/colour-120x40.txt
@@ -494,7 +494,7 @@
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Preferred regions^[[0m
 
  Tick the regions to keep, best first. Where a system has one BIOS per region, the best one found
-   is installed.
+   is installed. With none ticked, every region's BIOS is kept.
  
 ^[[0;7;35m > [1] North America^[[0m
    [ ] Japan
@@ -534,9 +534,12 @@
 === cores
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Cores^[[0m
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use: the platform's own
+   files are always kept.
  
-^[[0;7;35m > Filter (/ to type)^[[0m
+^[[0;7;35m > All^[[0m
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
  
@@ -568,10 +571,7 @@
  
  
  
- 
- 
- 
- ^[[0;1;35mA/Enter^[[0m Filter  ^[[0;2mB/Esc^[[0m Back  ^[[0;2mX/Space^[[0m Tick  ^[[0;2m?^[[0m Help
+ ^[[0;1;35mA/Enter^[[0m Tick all  ^[[0;2mB/Esc^[[0m Back  ^[[0;2mX/Space^[[0m Tick  ^[[0;2m?^[[0m Help
 === preview
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Preview^[[0m
 
diff --git a/tests/fixtures/tui/colour-40x12.txt b/tests/fixtures/tui/colour-40x12.txt
index b1eac105c..bbbf7d339 100644
--- a/tests/fixtures/tui/colour-40x12.txt
+++ b/tests/fixtures/tui/colour-40x12.txt
@@ -160,26 +160,26 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
  
 ^[[0;7;35m > [1] North America^[[0m
    [ ] Japan
  
- 
  ^[[0;1;35mA^[[0m Tick  ^[[0;2mB^[[0m Done  ^[[0;2m<>^[[0m Order  ^[[0;2m?^[[0m Help
 === cores
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Cores^[[0m
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
- 
-^[[0;7;35m > Filter (/ to type)^[[0m
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+^[[0;7;35m > All^[[0m
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
- 
- 
- 
- ^[[0;1;35mA^[[0m Filter  ^[[0;2mB^[[0m Back  ^[[0;2mX^[[0m Tick  ^[[0;2m?^[[0m Help
+ ^[[0;1;35mA^[[0m Tick all  ^[[0;2mB^[[0m Back  ^[[0;2mX^[[0m Tick  ^[[0;2m?^[[0m Help
 === preview
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Preview^[[0m
 
diff --git a/tests/fixtures/tui/colour-40x15.txt b/tests/fixtures/tui/colour-40x15.txt
index a1914ccc5..9430e9fbd 100644
--- a/tests/fixtures/tui/colour-40x15.txt
+++ b/tests/fixtures/tui/colour-40x15.txt
@@ -196,7 +196,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
  
 ^[[0;7;35m > [1] North America^[[0m
    [ ] Japan
@@ -204,24 +205,23 @@
  
  
  
- 
  ^[[0;1;35mA^[[0m Tick  ^[[0;2mB^[[0m Done  ^[[0;2m<>^[[0m Order  ^[[0;2m?^[[0m Help
 === cores
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Cores^[[0m
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
  
-^[[0;7;35m > Filter (/ to type)^[[0m
+^[[0;7;35m > All^[[0m
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
  
  
- 
- 
- 
- 
- ^[[0;1;35mA^[[0m Filter  ^[[0;2mB^[[0m Back  ^[[0;2mX^[[0m Tick  ^[[0;2m?^[[0m Help
+ ^[[0;1;35mA^[[0m Tick all  ^[[0;2mB^[[0m Back  ^[[0;2mX^[[0m Tick  ^[[0;2m?^[[0m Help
 === preview
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Preview^[[0m
 
diff --git a/tests/fixtures/tui/colour-80x24.txt b/tests/fixtures/tui/colour-80x24.txt
index 2501614e0..8c3fb5a3a 100644
--- a/tests/fixtures/tui/colour-80x24.txt
+++ b/tests/fixtures/tui/colour-80x24.txt
@@ -302,7 +302,8 @@
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Preferred regions^[[0m
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
  
 ^[[0;7;35m > [1] North America^[[0m
    [ ] Japan
@@ -321,14 +322,16 @@
  
  
  
- 
  ^[[0;1;35mA/Enter^[[0m Tick  ^[[0;2mB/Esc^[[0m Done  ^[[0;2mLeft/Right^[[0m Order  ^[[0;2m?^[[0m Help
 === cores
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Cores^[[0m
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
  
-^[[0;7;35m > Filter (/ to type)^[[0m
+^[[0;7;35m > All^[[0m
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
  
@@ -344,10 +347,7 @@
  
  
  
- 
- 
- 
- ^[[0;1;35mA/Enter^[[0m Filter  ^[[0;2mB/Esc^[[0m Back  ^[[0;2mX/Space^[[0m Tick  ^[[0;2m?^[[0m Help
+ ^[[0;1;35mA/Enter^[[0m Tick all  ^[[0;2mB/Esc^[[0m Back  ^[[0;2mX/Space^[[0m Tick  ^[[0;2m?^[[0m Help
 === preview
 ^[[0;1m ^[[0;1;35mRetroBIOS^[[0;1m: Preview^[[0m
 
diff --git a/tests/fixtures/tui/cores-120x40.txt b/tests/fixtures/tui/cores-120x40.txt
index d7a27d39c..571c06bea 100644
--- a/tests/fixtures/tui/cores-120x40.txt
+++ b/tests/fixtures/tui/cores-120x40.txt
@@ -1,8 +1,11 @@
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use: the platform's own
+   files are always kept.
 
- > Filter (/ to type)
+ > All
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -34,7 +37,4 @@
 
 
 
-
-
-
- A/Enter Filter  B/Esc Back  X/Space Tick  ? Help
+ A/Enter Tick all  B/Esc Back  X/Space Tick  ? Help
diff --git a/tests/fixtures/tui/cores-40x12.txt b/tests/fixtures/tui/cores-40x12.txt
index 0a09139e1..7557af130 100644
--- a/tests/fixtures/tui/cores-40x12.txt
+++ b/tests/fixtures/tui/cores-40x12.txt
@@ -1,12 +1,12 @@
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
-
- > Filter (/ to type)
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+ > All
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
-
-
-
- A Filter  B Back  X Tick  ? Help
+ A Tick all  B Back  X Tick  ? Help
diff --git a/tests/fixtures/tui/cores-40x15.txt b/tests/fixtures/tui/cores-40x15.txt
index 0015d8e99..5cbef31a7 100644
--- a/tests/fixtures/tui/cores-40x15.txt
+++ b/tests/fixtures/tui/cores-40x15.txt
@@ -1,15 +1,15 @@
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
 
- > Filter (/ to type)
+ > All
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
 
 
-
-
-
-
- A Filter  B Back  X Tick  ? Help
+ A Tick all  B Back  X Tick  ? Help
diff --git a/tests/fixtures/tui/cores-80x24.txt b/tests/fixtures/tui/cores-80x24.txt
index 1c98e53b5..c2fce774c 100644
--- a/tests/fixtures/tui/cores-80x24.txt
+++ b/tests/fixtures/tui/cores-80x24.txt
@@ -1,8 +1,11 @@
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
 
- > Filter (/ to type)
+ > All
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -18,7 +21,4 @@
 
 
 
-
-
-
- A/Enter Filter  B/Esc Back  X/Space Tick  ? Help
+ A/Enter Tick all  B/Esc Back  X/Space Tick  ? Help
diff --git a/tests/fixtures/tui/regions-120x40.txt b/tests/fixtures/tui/regions-120x40.txt
index 17076bca5..271fd15d7 100644
--- a/tests/fixtures/tui/regions-120x40.txt
+++ b/tests/fixtures/tui/regions-120x40.txt
@@ -1,7 +1,7 @@
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region, the best one found
-   is installed.
+   is installed. With none ticked, every region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
diff --git a/tests/fixtures/tui/regions-40x12.txt b/tests/fixtures/tui/regions-40x12.txt
index 077ec3344..70928bc8b 100644
--- a/tests/fixtures/tui/regions-40x12.txt
+++ b/tests/fixtures/tui/regions-40x12.txt
@@ -3,10 +3,10 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
 
-
  A Tick  B Done  <> Order  ? Help
diff --git a/tests/fixtures/tui/regions-40x15.txt b/tests/fixtures/tui/regions-40x15.txt
index ed7a42e45..fb7897ea1 100644
--- a/tests/fixtures/tui/regions-40x15.txt
+++ b/tests/fixtures/tui/regions-40x15.txt
@@ -3,7 +3,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
@@ -11,5 +12,4 @@
 
 
 
-
  A Tick  B Done  <> Order  ? Help
diff --git a/tests/fixtures/tui/regions-80x24.txt b/tests/fixtures/tui/regions-80x24.txt
index f34ca81a9..fe09f21c6 100644
--- a/tests/fixtures/tui/regions-80x24.txt
+++ b/tests/fixtures/tui/regions-80x24.txt
@@ -1,7 +1,8 @@
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
 
  > [1] North America
    [ ] Japan
@@ -20,5 +21,4 @@
 
 
 
-
  A/Enter Tick  B/Esc Done  Left/Right Order  ? Help
diff --git a/tests/fixtures/tui/route-evmapy.txt b/tests/fixtures/tui/route-evmapy.txt
index dea4a502d..757cd93ec 100644
--- a/tests/fixtures/tui/route-evmapy.txt
+++ b/tests/fixtures/tui/route-evmapy.txt
@@ -623,12 +623,12 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
 
-
  A Tick  B Done  <> Order
 === regions 40x15
  RetroBIOS: Preferred regions
@@ -636,7 +636,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
@@ -644,13 +645,13 @@
 
 
 
-
  A Tick  B Done  <> Order
 === regions 80x24
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
 
  > [1] North America
    [ ] Japan
@@ -669,43 +670,45 @@
 
 
 
-
  A Tick  B Done  Left/Right Order
 === cores 40x12
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
-
- > Filter (with a keyboard)
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === cores 40x15
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
 
-
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === cores 80x24
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -721,10 +724,7 @@
 
 
 
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === preview 80x24
  RetroBIOS: Preview
 
diff --git a/tests/fixtures/tui/route-gptokeyb.txt b/tests/fixtures/tui/route-gptokeyb.txt
index be42befe4..57e529f2c 100644
--- a/tests/fixtures/tui/route-gptokeyb.txt
+++ b/tests/fixtures/tui/route-gptokeyb.txt
@@ -623,12 +623,12 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
 
-
  A Tick  B Done  <> Order
 === regions 40x15
  RetroBIOS: Preferred regions
@@ -636,7 +636,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
@@ -644,13 +645,13 @@
 
 
 
-
  A Tick  B Done  <> Order
 === regions 80x24
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
 
  > [1] North America
    [ ] Japan
@@ -669,43 +670,45 @@
 
 
 
-
  A Tick  B Done  Left/Right Order
 === cores 40x12
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
-
- > Filter (with a keyboard)
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === cores 40x15
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
 
-
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === cores 80x24
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -721,10 +724,7 @@
 
 
 
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === preview 80x24
  RetroBIOS: Preview
 
diff --git a/tests/fixtures/tui/route-gptokeyb_muxterm.txt b/tests/fixtures/tui/route-gptokeyb_muxterm.txt
index cd39e4a38..7b58f1a18 100644
--- a/tests/fixtures/tui/route-gptokeyb_muxterm.txt
+++ b/tests/fixtures/tui/route-gptokeyb_muxterm.txt
@@ -623,12 +623,12 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
 
-
  A Tick  B Done  <> Order
 === regions 40x15
  RetroBIOS: Preferred regions
@@ -636,7 +636,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
@@ -644,13 +645,13 @@
 
 
 
-
  A Tick  B Done  <> Order
 === regions 80x24
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
 
  > [1] North America
    [ ] Japan
@@ -669,43 +670,45 @@
 
 
 
-
  A Tick  B Done  Left/Right Order
 === cores 40x12
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
-
- > Filter (with a keyboard)
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === cores 40x15
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
 
-
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === cores 80x24
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -721,10 +724,7 @@
 
 
 
-
-
-
- A Filter  B Back  X Tick
+ A Tick all  B Back  X Tick
 === preview 80x24
  RetroBIOS: Preview
 
diff --git a/tests/fixtures/tui/route-keys.txt b/tests/fixtures/tui/route-keys.txt
index 189f0f71e..27618219c 100644
--- a/tests/fixtures/tui/route-keys.txt
+++ b/tests/fixtures/tui/route-keys.txt
@@ -598,12 +598,12 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
 
-
  Enter Tick  Esc Done  <> Order  ? Help
 === regions 40x15
  RetroBIOS: Preferred regions
@@ -611,7 +611,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
@@ -619,13 +620,13 @@
 
 
 
-
  Enter Tick  Esc Done  <> Order  ? Help
 === regions 80x24
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
 
  > [1] North America
    [ ] Japan
@@ -644,43 +645,45 @@
 
 
 
-
  Enter Tick  Esc Done  Left/Right Order  ? Help
 === cores 40x12
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
-
- > Filter (/ to type)
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+ > All
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
-
-
-
- Enter Filter  Esc Back  Space Tick
+ Enter Tick all  Esc Back  Space Tick
 === cores 40x15
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
 
- > Filter (/ to type)
+ > All
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
 
 
-
-
-
-
- Enter Filter  Esc Back  Space Tick
+ Enter Tick all  Esc Back  Space Tick
 === cores 80x24
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
 
- > Filter (/ to type)
+ > All
+   None
+   Filter (/ to type)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -696,10 +699,7 @@
 
 
 
-
-
-
- Enter Filter  Esc Back  Space Tick  ? Help
+ Enter Tick all  Esc Back  Space Tick  ? Help
 === preview 40x12
  RetroBIOS: Preview
 
diff --git a/tests/fixtures/tui/route-miyoo.txt b/tests/fixtures/tui/route-miyoo.txt
index 5b9098ff5..80d5b8cbd 100644
--- a/tests/fixtures/tui/route-miyoo.txt
+++ b/tests/fixtures/tui/route-miyoo.txt
@@ -652,12 +652,12 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
 
-
  A Tick  R2 Done  <> Order
 === regions 40x15
  RetroBIOS: Preferred regions
@@ -665,7 +665,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
@@ -673,13 +674,13 @@
 
 
 
-
  A Tick  R2 Done  <> Order
 === regions 80x24
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
 
  > [1] North America
    [ ] Japan
@@ -698,43 +699,45 @@
 
 
 
-
  A Tick  R2 Done  Left/Right Order
 === cores 40x12
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
-
- > Filter (with a keyboard)
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
-
-
-
- A Filter  R2 Back
+ A Tick all  R2 Back
 === cores 40x15
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
 
-
-
-
-
- A Filter  R2 Back
+ A Tick all  R2 Back
 === cores 80x24
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
 
- > Filter (with a keyboard)
+ > All
+   None
+   Filter (with a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -750,10 +753,7 @@
 
 
 
-
-
-
- A Filter  R2 Back
+ A Tick all  R2 Back
 === preview 80x24
  RetroBIOS: Preview
 
diff --git a/tests/fixtures/tui/route-muxterm.txt b/tests/fixtures/tui/route-muxterm.txt
index 05260a80f..1ad851b69 100644
--- a/tests/fixtures/tui/route-muxterm.txt
+++ b/tests/fixtures/tui/route-muxterm.txt
@@ -652,12 +652,12 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
 
-
  Start Tick  B Done  <> Order
 === regions 40x15
  RetroBIOS: Preferred regions
@@ -665,7 +665,8 @@
  Tick the regions to keep, best first.
    Where a system has one BIOS per
    region, the best one found is
-   installed.
+   installed. With none ticked, every
+   region's BIOS is kept.
 
  > [1] North America
    [ ] Japan
@@ -673,13 +674,13 @@
 
 
 
-
  Start Tick  B Done  <> Order
 === regions 80x24
  RetroBIOS: Preferred regions
 
  Tick the regions to keep, best first. Where a system has one BIOS per region,
-   the best one found is installed.
+   the best one found is installed. With none ticked, every region's BIOS is
+   kept.
 
  > [1] North America
    [ ] Japan
@@ -698,43 +699,45 @@
 
 
 
-
  Start Tick  B Done  Left/Right Order
 === cores 40x12
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
-
- > Filter (Select shows a keyboard)
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
+ > All
+   None
+   Filter (Select shows a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
-
-
-
- Start Filter  B Back  Y Tick
+ Start Tick all  B Back  Y Tick
 === cores 40x15
  RetroBIOS: Cores
 
- Tick the cores you use. With none
-   ticked, every core's files are kept.
+ Every core ticked keeps every core's
+   files. Untick the cores you do not
+   use: the platform's own files are
+   always kept.
 
- > Filter (Select shows a keyboard)
+ > All
+   None
+   Filter (Select shows a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
 
-
-
-
-
- Start Filter  B Back  Y Tick
+ Start Tick all  B Back  Y Tick
 === cores 80x24
  RetroBIOS: Cores
 
- Tick the cores you use. With none ticked, every core's files are kept.
+ Every core ticked keeps every core's files. Untick the cores you do not use:
+   the platform's own files are always kept.
 
- > Filter (Select shows a keyboard)
+ > All
+   None
+   Filter (Select shows a keyboard)
    [ ] mesen
    [x] pcsx_rearmed
 
@@ -750,10 +753,7 @@
 
 
 
-
-
-
- Start Filter  B Back  Y Tick
+ Start Tick all  B Back  Y Tick
 === preview 40x12
  RetroBIOS: Preview
 
diff --git a/tests/test_install_from.py b/tests/test_install_from.py
index 2ddb97e7e..ff28c52c7 100644
--- a/tests/test_install_from.py
+++ b/tests/test_install_from.py
@@ -148,7 +148,7 @@ class CopyFromAnOldCard(FromFolder):
         proc = self.install()
         self.assertEqual(proc.returncode, 1, proc.stdout + proc.stderr)
         self.assertEqual(self.installed(), {"scph5500.bin": JP, "pcsx/extra.bin": EXTRA})
-        self.assertIn(f"2 files copied from {self.old}, 2 still missing.", proc.stdout)
+        self.assertIn(f"2 files copied from {self.old}, 2 failed.", proc.stdout)
 
     def test_a_link_out_of_the_folder_is_not_followed(self):
         outside = self.root / "elsewhere"
@@ -196,7 +196,7 @@ class CopyFromAnOldCard(FromFolder):
             (repo.root / "bios" / "mgba_extra.bin").unlink()
             proc = repo.run("--from", str(old), "--no-input")
             self.assertEqual(proc.returncode, 1, proc.stdout + proc.stderr)
-            self.assertIn(f"2 files copied from {old}, 2 downloaded, 1 still missing.",
+            self.assertIn(f"2 files copied from {old}, 2 downloaded, 1 failed.",
                           proc.stdout)
             self.assertEqual(sorted(repo.installed()), sorted(
                 name for name in payloads if name != "mgba/extra.bin"))
diff --git a/tests/test_install_tui.py b/tests/test_install_tui.py
index 96602a56e..f4cf5099a 100644
--- a/tests/test_install_tui.py
+++ b/tests/test_install_tui.py
@@ -527,18 +527,20 @@ class Flow(unittest.TestCase):
         state.focus["options"] = 3
         press(state, "enter")
         self.assertEqual(state.screen, "cores")
-        self.assertEqual([row.value for row in install.tui_rows(state)][1:],
+        self.assertEqual([row.value for row in install.tui_rows(state)][3:],
                          ["mesen", "pcsx_rearmed"])
         self.assertEqual(install.tui_rows(state)[state.focus["cores"]].value, "mesen")
+        # Every core ticked while none narrows the run: one untick keeps
+        # the others, ticked back it is every core again.
         press(state, " ")
-        self.assertEqual(state.cores, ["mesen"])
-        press(state, "left")
+        self.assertEqual(state.cores, ["pcsx_rearmed"])
+        press(state, "right")
         self.assertEqual(state.cores, [])
         press(state, "/", "p", "c")
-        self.assertEqual([row.value for row in install.tui_rows(state)][1:], ["pcsx_rearmed"])
-        press(state, "enter", "right", "enter")
+        self.assertEqual([row.value for row in install.tui_rows(state)][3:], ["pcsx_rearmed"])
+        press(state, "enter", "left", "enter")
         self.assertEqual(state.screen, "options")
-        self.assertEqual(install.tui_flags(state), [("--core", "pcsx_rearmed")])
+        self.assertEqual(install.tui_flags(state), [("--core", "mesen")])
 
     def test_preview_is_a_dry_run(self):
         state = checked_state()
@@ -13855,6 +13857,81 @@ class AuditTwentyThreeAndSixteen(unittest.TestCase):
                 self.assertIn("reads its BIOS files", small)
                 self.assertIn(folder[-12:], small)
 
+    # The owner's note: Cores drew every box empty when no core narrows the
+    # run, read as "nothing is ticked, tick them all".
+
+    def cores_screen(self, **given) -> install.TuiState:
+        state = checked_state()
+        state.cores = list(given.get("cores", []))
+        state.cli_cores = list(state.cores)
+        press(state, "o")
+        state.focus["options"] = next(index for index, row in enumerate(
+            install.tui_rows(state)) if row.action == "cores")
+        press(state, "enter")
+        self.assertEqual(state.screen, "cores")
+        return state
+
+    @staticmethod
+    def boxes(state: install.TuiState) -> dict:
+        return {row.value: row.label[:3] for row in install.tui_rows(state)
+                if row.action == "core"}
+
+    def test_cores_open_every_one_ticked(self):
+        state = self.cores_screen()
+        self.assertEqual(self.boxes(state), {"mesen": "[x]", "pcsx_rearmed": "[x]"})
+        self.assertEqual(install.tui_rows(state)[state.focus["cores"]].value, "mesen")
+        self.assertEqual(install.tui_flags(state), [])
+
+    def test_one_untick_narrows_to_the_others(self):
+        state = self.cores_screen()
+        press(state, " ")
+        self.assertEqual(self.boxes(state), {"mesen": "[ ]", "pcsx_rearmed": "[x]"})
+        self.assertEqual(install.tui_flags(state), [("--core", "pcsx_rearmed")])
+        press(state, " ")
+        self.assertEqual(self.boxes(state), {"mesen": "[x]", "pcsx_rearmed": "[x]"})
+        self.assertEqual(state.cores, [])
+        press(state, " ", "enter")
+        self.assertEqual(state.screen, "options")
+        row = next(row for row in install.tui_rows(state) if row.action == "cores")
+        self.assertEqual(row.label, "Cores: 1 of 2")
+        state.stack = ["setup", "plan"]
+        self.assertIn("1 of 2 cores", " ".join(install.tui_view(state, 100, 30)))
+
+    def test_none_then_all_as_the_systems_list(self):
+        state = self.cores_screen()
+        rows = install.tui_rows(state)
+        state.focus["cores"] = next(i for i, row in enumerate(rows) if row.action == "none")
+        press(state, "enter")
+        self.assertEqual(self.boxes(state), {"mesen": "[ ]", "pcsx_rearmed": "[ ]"})
+        press(state, "enter")
+        self.assertEqual(state.screen, "cores")
+        self.assertIn("No core is ticked", str(state.status))
+        state.focus["cores"] = next(i for i, row in enumerate(rows) if row.action == "all")
+        press(state, "enter")
+        self.assertEqual(self.boxes(state), {"mesen": "[x]", "pcsx_rearmed": "[x]"})
+        self.assertEqual(install.tui_flags(state), [])
+
+    def test_core_ticks_only_the_cores_it_names(self):
+        state = self.cores_screen(cores=["pcsx_rearmed"])
+        self.assertEqual(self.boxes(state), {"mesen": "[ ]", "pcsx_rearmed": "[x]"})
+        state.stack = ["setup", "plan"]
+        self.assertIn("--core", " ".join(install.tui_view(state, 100, 30)))
+
+    def test_both_modes_count_the_cores_kept_alike(self):
+        listing = self.listing("retroarch", [
+            self.entry("a.bin", b"A" * 8, ["nintendo-gba"]),
+            self.entry("m.bin", b"M" * 8, ["nintendo-gba"], cores=["mgba"]),
+            self.entry("v.bin", b"V" * 8, ["nintendo-gba"], cores=["vba_next"]),
+            self.entry("p.bin", b"P" * 8, ["sony-playstation"])])
+        text, _asked = self.line_run(_args(manifest=listing, dest=self.here,
+                                           declared_only=False, dry_run=True),
+                                     ["c", "", "2"])
+        self.assertIn("Every core's extra files are kept: Enter keeps them all", text)
+        head = text.rsplit("Counted again for your choices", 1)[1]
+        self.assertIn("1 of 2 cores", head)
+        self.assertEqual(install.cores_words(0, 2), "all cores")
+        self.assertEqual(install.cores_words(2, 2), "all cores")
+
     # Root cause 6: the pages say what the installer shows.
 
     def test_which_pack_names_the_first_screen(self):
diff --git a/wiki/installer.md b/wiki/installer.md
index cd21730d0..19531cdeb 100644
--- a/wiki/installer.md
+++ b/wiki/installer.md
@@ -770,7 +770,11 @@ answer is not asked.
   chosen too, as `generate_pack.py --system` does.
 - **Cores.** The platform's own BIOS list for the chosen systems is always
   kept. This narrows only the extra files each emulator core loads beyond it.
-  Asked only when the chosen systems have such files.
+  Asked only when the chosen systems have such files. Every core is kept
+  until numbers name some, and the head then says how many of how many
+  (`1 of 2 cores`). The full screen's **Cores** opens with every core
+  ticked, as Choose systems does: untick the ones you do not use, **All**
+  and **None** tick or untick them all.
 - **Regions.** Asked only when a chosen system has one BIOS per region. The
   numbers give an order of preference: `2,1` keeps the second region where a
   file for it exists, and the first one elsewhere.