EES writes 'c' where a figure is withheld and the categories sum to the
cohort, so counts and percentages are emitted as text with the sentinel
intact. safe_numeric must never be pointed at them.
School rows and the England reference need different establishment pins:
at national level selective schools, studios and UTCs are separate
populations rather than labels, so leaving establishment open multiplies
30 rows into 190. Two queries per period, each keeping its own level.
Verified against the live API for 2022/23: 135,240 school records over
4,508 schools, exactly 30 each, no duplicate keys, 31,382 sentinels kept.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BvdDKvFFSZuMVDH5fEyTob
