split-resolution-a-part

Date: 2026-09-11. Status: superseded.

Decision. When several split parts of a postcode are valid, every lookup resolves to the A part by default and reports status a_part. A split="report" rule returns split_consensus or split_conflict instead. The result's label records which rule was used. Python and SQL are tested to agree under both.

Reason. NRS builds the Scottish Statistics Postcode Lookup by converting split postcodes to the A part, because A is the part with more addresses, so every official statistic uses that convention. Matching it by default means an analyst reconciling against official figures gets the same answer; the report rule keeps the ambiguity visible for anyone who wants it. Supersedes the never-choose-A rule of lookup-statuses.

Evidence. NRS Scottish Statistics Postcode Lookup information note; SPD 2026/2 bulletin on suffix ordering; docs/NRS_GUIDANCE_CHECK.md. On the synthetic cohort, 56 events resolve as a_part.