Add registry reference rows for event identity coverage

schema/dataset/v1/NORMALIZATION.md

@@ -46,13 +46,15 @@ The validated private staging build is at:
 - Source revision:
   `ee9f6ea859af22f448b6b8257c657c2e63e42cefb00a487e639c405a10d79377`
 - Normalization manifest SHA-256:
-  `3f4b19dc7719daa11865e83d878bb8d89d712d042b2b18474b6465f2db073e17`
-- Local footprint: 93 MiB
-- Valid normalized rows: 120,348
+  `3fad8e709ef2eb1d5d31661bfff52df50954a3167908e4d6aee36a2ba280bb02`
+- Local footprint: 95 MiB
+- Valid normalized rows: 122,467
 - Companies: 4,160
 - Documents: 76,362, plus two reason-coded missing-date quarantines
-- Dated instrument positions: 8,776 (6,991 active/current plus 1,785
-  explicitly pending positions used by the live screener)
+- Instrument rows: 10,895 — 8,776 dated position assertions (6,991
+  active/current plus 1,785 explicitly pending positions used by the live
+  screener) and 2,119 reference-only registry identities with null quantity so
+  every event instrument resolves without inventing a position or zero value.
 - Events: 31,050, plus one fractional-share quarantine
 - Deterministic legacy inference: 165 historical position rows defaulted to
   active because the source snapshot asserted their presence.