which-table-answers-which-question

Date: 2026-09-12. Status: implemented.

Decision. Python date-valid lookups (on=, attach with a date column, attach_by_era) and split-report requests need SPD history and are refused against SSPL. Default SQL uses own-record SSPL geography and an analysis year to select the edition, returning both publishers and address warnings. Legacy SPD SQL is isolated under docs/sql/history. Python remains current-only/as-of with own-record geography and sentinel exclusion. Both stored tables retain source values for PO boxes and unlinked large users; consumers apply their documented exclusions.

Reason. One latest life per postcode cannot say whether a postcode existed at a date or which zone it was in then. Making the refusal explicit prevents a silent wrong answer. The split and PO-box defaults are unchanged so existing consumers see the same policy.

Evidence. SSPL dictionary: no small-user split postcodes; A part used; counts added. SSPL 2026/1 links: NO LINKP on 27,162 large users, NO LINK on 5, 15,368 real links of which 9 keep an A suffix.