Beechwood College (URN 142458, Sully, CF64 5SE) survived the England-only
filter. GIAS types it a Special post 16 institution (32), not a Welsh
establishment (30), so filtering on establishment type alone left it behind —
the last Welsh school on the site, and the reason Vale of Glamorgan was still
in the authority list.
The earlier verification claimed the type codes mapped onto the Welsh
authorities in both directions. That was checked exhaustively for Cardiff and
by count for three others; Vale of Glamorgan was never checked, and it was the
one that did not hold.
LA code is the reliable discriminator: GIAS gives the 22 Welsh unitary
authorities the contiguous block 660-681, which English authorities never use.
Filtering on postcode would have been wrong — Redbrook, Tutshill, Wyedean and
two other Gloucestershire schools carry NP16/NP25 postcodes because Royal Mail
areas straddle the border, and they are English schools with English data. An
e2e test now pins those five so the fix cannot be simplified into a postcode
filter later.
The 660-681 range is documented GIAS structure this project cannot verify from
its own data, so the range filters and the authority NAME checks: if the range
is ever wrong, a Welsh authority reappears in assert_england_only_schools and
the pipeline fails loudly.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj
