When statistics outlive their geography: asynchronous propagation of a secondary medical area redefinition across Japan's national health data infrastructure — a measurable instance of institutional debt

<p>Health-system geographies are periodically redefined, but the national statistical products that encode them are updated on independent schedules. We report a natural experiment in how such a redefinition propagates. Effective 1 April 2024, Akita Prefecture consolidated its secondary medical areas (SMAs) from eight to three — the only SMA reorganization under Japan’s 8th Medical Plan cycle — reducing the national SMA count from 335 to 330. We examined how three national data products required for SMA-level analysis of the same reference year (2024) encoded the change, by comparing their SMA code sets and validating municipal re-aggregations against published totals. The Physician, Dentist and Pharmacist Statistics 2024 (census date 31 December 2024; released December 2025) and the Ministry of Health, Labour and Welfare’s municipality–SMA correspondence table (version dated April 2026) encode the new three-SMA definition. The 11th NDB Open Data, released June 2026, tabulates fiscal-year 2024 claims — all generated after the redefinition took effect — in the superseded eight-SMA geography. No product declares the vintage of its zone definition as metadata; the divergence surfaces only as unexplained code mismatches — and, for three zone codes reused across definitions, as silent mis-joins — observable from published artifacts alone. We interpret this as a measurable instance of institutional debt — the divergence between legally effective definitions and those encoded in infrastructure, with reconciliation labor externalized to analysts — quantifiable along three axes (lag, affected population, repairability). Contrasting England’s centrally remapped response to its 2022 commissioning-geography transition, we propose that zone-level statistics be published as versioned views over stable unit identifiers with mandatory definition-vintage metadata.</p>