British Columbia's move to permanent Pacific Daylight Time (UTC-7) starting March 2026 creates a real data integrity problem for PostgreSQL users storing future timestamps. The `timestamptz` type stores UTC and reconverts using current timezone rules, so appointments stored before a `tzdata` update will return incorrect local times after the update. A SQL query is provided to check whether your `tzdata` has already been updated. The recommended solution is a dual-column pattern storing the wall-clock local time, the IANA timezone name, and a trigger-computed UTC timestamp separately. This preserves user intent and allows recomputation when timezone rules change. RFC 9557 explicitly does not solve this problem. A remediation checklist is also provided for cases where `tzdata` has already been updated and data may be corrupted.
