diff --git a/platforms/_shared.yml b/platforms/_shared.yml
index 9d27a273..23f1c106 100644
--- a/platforms/_shared.yml
+++ b/platforms/_shared.yml
@@ -163,22 +163,15 @@ shared_groups:
   # QUASI88 searches "quasi88/" subfolder first
   # ref: quasi88-libretro/src/LIBRETRO/libretro.c:463 — snprintf(..., "%s%cquasi88%c%s", ...)
   quasi88:
-    - name: N88.ROM
-      destination: quasi88/N88.ROM
-      required: true
-      md5: "4f984e04a99d56c4cfe36115415d6eb8"
-    - name: N88SUB.ROM
-      destination: quasi88/N88SUB.ROM
-      required: true
-      md5: "793f86784e5608352a5d7f03f03e0858"
-    - name: N88N.ROM
-      destination: quasi88/N88N.ROM
-      required: true
-      md5: "2ff07b8769367321128e03924af668a0"
-    - name: N88KNJ1.ROM
-      destination: quasi88/N88KNJ1.ROM
-      required: true
-      md5: "d81c6d5d7ad1a4bbbd6ae22a01257603"
+    # Only what System.dat does not declare for nec-pc-88: the mkII SR
+    # extension ROMs that match N88.ROM (MAME pc8801mk2sr: 710a63ec, c0bd2aa6,
+    # af2b6efa, 7713c519). The core reads N88EXTn.ROM before n88_n.rom
+    # (src/LIBRETRO/libretro.c:109-112), so they win over the n88_n.rom dumps
+    # System.dat pairs with that main ROM, which come from other models (n88_0
+    # 61984bab is the original PC-8801's). N88SUB.ROM, N88.ROM, N88N.ROM and
+    # N88KNJ1.ROM are the native disk.rom, n88.rom, n88n.rom and n88knj1.rom
+    # under the other spelling the core tries: aliases in the profile, not
+    # files of their own here, or the pack carried disk.rom twice.
     - name: N88EXT0.ROM
       destination: quasi88/N88EXT0.ROM
       required: true
@@ -195,27 +188,6 @@ shared_groups:
       destination: quasi88/N88EXT3.ROM
       required: true
       md5: "fc4b76a402ba501e6ba6de4b3e8b4273"
-    # N88EXT0-3.ROM above are the mkII SR extension ROMs that match N88.ROM
-    # (MAME pc8801mk2sr: 710a63ec, c0bd2aa6, af2b6efa, 7713c519). The core
-    # reads N88EXTn.ROM before n88_n.rom (src/LIBRETRO/libretro.c:109-112),
-    # so they win over the n88_n.rom dumps System.dat pairs with that main ROM,
-    # which come from other models (n88_0 61984bab is the original PC-8801's).
-    - name: n88_0.rom
-      destination: quasi88/n88_0.rom
-      required: false
-      md5: "e28fe3f520bea594350ea8fb00395370"
-    - name: n88_1.rom
-      destination: quasi88/n88_1.rom
-      required: false
-      md5: "a8e298da7ac947669bcb1ff25cee0a83"
-    - name: n88_2.rom
-      destination: quasi88/n88_2.rom
-      required: false
-      md5: "9d03154fd9abfc28c4e6d4dc705e6e23"
-    - name: n88_3.rom
-      destination: quasi88/n88_3.rom
-      required: false
-      md5: "e1791f8154f1cdf22b576a1a365b6e1f"
 
   # Sinclair ZX Spectrum — Fuse core (Pentagon/Scorpion ROMs)
   # VERIFIED: fuse-libretro/src/compat/paths.c compat_get_next_path()
diff --git a/tests/test_shared_groups.py b/tests/test_shared_groups.py
new file mode 100644
index 00000000..6592700c
--- /dev/null
+++ b/tests/test_shared_groups.py
@@ -0,0 +1,65 @@
+"""A shared group adds files, never a second name for a native one.
+
+The quasi88 group declared N88SUB.ROM beside the disk.rom System.dat
+already names for nec-pc-88, same bytes: the RetroArch pack carried the
+2 KB ROM twice under quasi88/, and the group read as twelve required files
+where four did the work. Alternative names are aliases in the profile.
+"""
+
+from __future__ import annotations
+
+import sys
+import unittest
+from pathlib import Path
+
+import yaml
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(REPO_ROOT / "scripts"))
+
+from common import list_registered_platforms, load_platform_config  # noqa: E402
+
+PLATFORMS = str(REPO_ROOT / "platforms")
+
+
+def _md5s(entry: dict) -> set[str]:
+    raw = entry.get("md5") or ""
+    values = raw if isinstance(raw, list) else str(raw).split(",")
+    return {v.strip().lower() for v in values if v and v.strip()}
+
+
+class SharedGroupsAddOnly(unittest.TestCase):
+    def test_no_shared_file_repeats_a_native_file_of_the_same_directory(self):
+        shared = yaml.safe_load((REPO_ROOT / "platforms" / "_shared.yml").read_text())
+        groups = shared.get("shared_groups") or {}
+        repeated = []
+        for platform in list_registered_platforms(PLATFORMS, include_archived=True):
+            config = load_platform_config(platform, PLATFORMS)
+            for system in config.get("systems", {}).values():
+                included = [
+                    fe for group in system.get("includes", []) for fe in groups.get(group, [])
+                ]
+                if not included:
+                    continue
+                group_keys = {
+                    (fe.get("name"), fe.get("destination", fe.get("name"))) for fe in included
+                }
+                native: dict[tuple[str, str], str] = {}
+                for fe in system.get("files", []):
+                    if (fe.get("name"), fe.get("destination", fe.get("name"))) in group_keys:
+                        continue
+                    dest = fe.get("destination") or fe.get("name", "")
+                    directory = dest.rsplit("/", 1)[0] if "/" in dest else ""
+                    for md5 in _md5s(fe):
+                        native.setdefault((directory, md5), fe.get("name", ""))
+                for fe in included:
+                    dest = fe.get("destination") or fe.get("name", "")
+                    directory = dest.rsplit("/", 1)[0] if "/" in dest else ""
+                    for md5 in _md5s(fe):
+                        other = native.get((directory, md5))
+                        if other and other.lower() != fe.get("name", "").lower():
+                            repeated.append(f"{platform}:{fe['name']} = {other}")
+        self.assertEqual(repeated, [])
+
+if __name__ == "__main__":
+    unittest.main()