diff --git a/docs/HANDOVER_API_PROFILING.md b/docs/HANDOVER_API_PROFILING.md
index 426db63c..7edf26fa 100644
--- a/docs/HANDOVER_API_PROFILING.md
+++ b/docs/HANDOVER_API_PROFILING.md
@@ -437,6 +437,36 @@ table. **Verified 0/909 corpus raises; eval unchanged 54.9%/909/0** — pure fut
   `u_roof` (→0.4). The `age_band is None` branches above each are justified absent-data defaults;
   only a typo/unknown band silently passing is the gap.
 
+### SESSION-9 (cont. 2) — glazing single/secondary/triple per RdSAP 10 Table 24, `a0432977` (BIGGEST WIN)
+Chasing Tier-2 turned up the session's biggest lever. `_API_GLAZING_TYPE_TO_TRANSMISSION` mapped
+only the DOUBLE-glazing codes [1,2,3,13,14]; single (5/15), secondary (4/11/12), triple
+(6/8/9/10) returned None → the cascade routed them to the `u_window` all-None default **U=2.5**
+instead of their Table 24 value. **Single glazing (U=4.8) modelled at half its heat loss** was
+the killer — 79 corpus certs carry code 5; the 94 certs with any unmapped glazing code sat at
+**32% within-0.5 vs 54.9% baseline**. Extended the transmission + gap-override tables with the
+RdSAP 10 Table 24 (spec p.50) (U, g, FF) rows for every RdSAP-21 glazing code. **Eval 54.90% →
+56.66% within-0.5** (net +16: 22 in, 6 offsetting-error out), within-1.0 70.2→71.9, mean|err|
+1.224→1.203, 909/0. 7 AAA tests, goldens + gate green, pyright net-zero. **Method that found it:
+profile by `sap_windows[].glazing_type`, split known vs unmapped codes, decode against
+`epc_codes.csv` `glazed_type`.**
+
+### OPEN — KNOWN bugs still on the board (ranked)
+1. **Glazing SOLAR/LIGHT g mis-keyed** (the natural follow-on): `_G_PERPENDICULAR_BY_GLAZING_TYPE`
+   (solar_gains.py) + `_G_LIGHT_BY_GLAZING_CODE` (internal_gains.py) are keyed on the SAP-10.2
+   Table-6b cascade ordering (1=single…) but `_api_cascade_glazing_type` only translates {1:2} —
+   every OTHER API code passes through UNTRANSLATED, so API code 5 (single) reads the cascade-5
+   slot (secondary/DG-low-E g) for solar+daylight gains. Smaller than the U effect (gains are
+   second-order) but a real systematic mis-map. Fix = complete `_api_cascade_glazing_type` →
+   Table-6b, OR feed the transmission-tuple g instead. Verify magnitude first.
+2. **Window orientation silently dropped** (solar_gains.py:391 `if orientation is None: continue`)
+   — an unmapped orientation code loses the whole window's solar gain. HIGH-confidence data-loss.
+3. **Tier-2 glazing strict-raise** — now that codes 1-15 are mapped, make `_api_glazing_transmission`
+   raise `UnmappedApiCode` on a present-but-unmapped (>15) code (zero current regression).
+4. Tier-3 age-band swallows (low impact). MVHR (mech_vent=4) deferred. 21.0.0 builder missing the
+   8/8b/8c ventilation + (now) glazing edits — extend if a 21.0.0 cert surfaces.
+5. Per-cert: cert 0370-2933 still +15 after glazing (7 single windows but the over-rate is
+   non-window — separate fabric/heating cause). The 100 unsupported-schema certs (big ticket).
+
 ## THE 100 unsupported_schema CERTS (deferred — bigger ticket)
 SAP-Schema-19.1.0 (and other pre-21). The user is planning a separate big piece: map old schemas
 → new + **predict missing fields from similar-looking properties** (needs an EPC-prediction