diff --git a/scripts/generate_pack.py b/scripts/generate_pack.py
index 2b81570b..e97ea4df 100644
--- a/scripts/generate_pack.py
+++ b/scripts/generate_pack.py
@@ -3568,6 +3568,43 @@ def _manifest_selection(
     )
 
 
+def _record_absent(
+    absent: list[dict],
+    config: dict,
+    base_dest: str,
+    region_drops: set,
+    required_only: bool,
+    seen_destinations: set,
+    omitted_by_destination: dict,
+    record_omission,
+) -> None:
+    """A file a core needs that the collection does not hold is an omission.
+
+    Left out of both lists, DevilutionX's diabdat.mpq and dhewm3's
+    pak000-004 reached no safety notice: the installer said everything
+    was verified and the game refused to start.
+    """
+    extras_pfx = _detect_extras_prefix(config, base_dest)
+    for fe in absent:
+        if required_only and fe.get("required") is False:
+            continue
+        dest = sanitize_pack_path(fe.get("destination", fe.get("name", "")))
+        if not dest or (region_drops and dest in region_drops):
+            continue
+        full_dest = (
+            dest if not extras_pfx or dest.startswith(f"{extras_pfx}/")
+            else f"{extras_pfx}/{dest}"
+        )
+        if full_dest in seen_destinations or full_dest in omitted_by_destination:
+            continue
+        source_emu = fe.get("source_profile") or fe.get("source_emulator", "")
+        systems = _extra_system_ids(fe)
+        record_omission(
+            full_dest, fe, systems[0] if systems else "", "not_found",
+            [source_emu] if source_emu else [],
+        )
+
+
 def _record_unplaceable(unplaceable: list[dict], record_omission) -> None:
     """Held by the collection, nowhere to put it on this platform.
 
@@ -3879,6 +3916,7 @@ def generate_manifest(
     # Phase 2: core complement (emulator extras)
     unplaceable: list[dict] = []
     baseline_claims: dict[str, dict] = {}
+    absent: list[dict] = []
     if source != "platform":
         core_files = _collect_emulator_extras(
             config,
@@ -3891,10 +3929,15 @@ def generate_manifest(
             include_all=(source == "truth"),
             unplaceable=unplaceable,
             baseline_claims=baseline_claims,
+            absent=absent,
         )
     else:
         core_files = []
     _record_unplaceable(unplaceable, record_omission)
+    _record_absent(
+        absent, config, base_dest, region_drops, required_only,
+        seen_destinations, omitted_by_destination, record_omission,
+    )
     total_size += _manifest_core_entries(
         core_files, config, db, bios_dir, base_dest, repo_root,
         zip_contents, offline, region_drops, case_insensitive,
diff --git a/tests/test_core_file_fills_declaration.py b/tests/test_core_file_fills_declaration.py
index 67e1f2de..34ed15fc 100644
--- a/tests/test_core_file_fills_declaration.py
+++ b/tests/test_core_file_fills_declaration.py
@@ -182,5 +182,46 @@ class AMissingDataDirectoryFailsTheRun(unittest.TestCase):
         self.assertEqual(stop.exception.code, 1)
 
 
+
+class AFileNobodyHoldsIsAnOmission(unittest.TestCase):
+    """DevilutionX's diabdat.mpq, required and not in the collection, was
+    in neither the manifest's files nor its omitted_files: the installer
+    showed no notice and said everything was verified."""
+
+    def test_the_manifest_names_it(self):
+        from generate_pack import generate_manifest
+
+        _emulator_profiles_cache.clear()
+        root = Path(tempfile.mkdtemp(dir=REPO_ROOT / "tmp"))
+        self.addCleanup(shutil.rmtree, root, True)
+        for folder in ("platforms", "emulators", "bios"):
+            (root / folder).mkdir()
+        (root / "platforms" / "fakeplat.yml").write_text(yaml.safe_dump({
+            "platform": "FakePlat", "verification_mode": "existence",
+            "base_destination": "system", "cores": ["devil"],
+            "systems": {"diablo": {"files": []}},
+        }))
+        (root / "platforms" / "_registry.yml").write_text(yaml.safe_dump({
+            "platforms": {"fakeplat": {"config": "fakeplat.yml", "status": "active"}},
+        }))
+        (root / "emulators" / "devil.yml").write_text(yaml.safe_dump({
+            "emulator": "Devil", "type": "libretro", "cores": ["devil"],
+            "systems": ["diablo"],
+            "files": [{"name": "diabdat.mpq", "required": True,
+                       "sha1": "1" * 40, "category": "game_data"}],
+        }))
+        db = {"files": {}, "indexes": {"by_md5": {}, "by_name": {}, "by_crc32": {},
+                                      "by_path_suffix": {}}}
+        manifest = generate_manifest(
+            "fakeplat", str(root / "platforms"), db, str(root / "bios"),
+            str(root / "platforms" / "_registry.yml"),
+            emulators_dir=str(root / "emulators"), offline=True,
+        )
+        omitted = {o["name"]: o for o in manifest["omitted_files"]}
+        self.assertIn("diabdat.mpq", omitted)
+        self.assertTrue(omitted["diabdat.mpq"]["required"])
+        self.assertEqual(omitted["diabdat.mpq"]["reason"], "not_found")
+
+
 if __name__ == "__main__":
     unittest.main()