diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index fc2a9615..56315404 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -3186,7 +3186,13 @@ def _synthesise_19_0_sap_windows(schema: RdSapSchema19_0) -> List[SapWindow]:
     core (976/1000 band-1 with no measured band-1 windows; only 6 rich certs).
     19.0 glazed_type codes (observed 1-4, 6, 7) are a subset of 20.0.0's verified
     1-8 space: route integer codes through the verified cascade; the "ND" string
-    falls back to the DG-modal default. Own seam so 19.0 can diverge."""
+    falls back to the DG-modal default. Own seam so 19.0 can diverge.
+
+    Transfer note (ADR-0028 validate-don't-re-fit): 19.0's band-4 Validation
+    Cohort (n=6) observes a glazing/floor ratio of 0.178 vs the inherited
+    prediction 0.223 — a ~20% under-run, weaker than 18.0's exact match. Left
+    inherited (n=6, all band-4, no band-1 to fit); revisit only if synthesis
+    fidelity (scoring) ever needs it. `scripts/eon/profile_corpus.py` regenerates."""
     mgt = schema.multiple_glazing_type
     glazing_type = (
         _api_cascade_glazing_type(mgt)