PostgreSQL

PostgreSQL’s per-release notes carry “Migration to N” and “Known regressions” sections. The Postgres community’s discipline on documenting breakage is one of the genre’s high-water marks; the notes for any major version include a dedicated section on incompatibilities with the previous version, with the specific extension and query patterns affected.

This is the format every long-lived software project should aspire to. Decades of release notes, all consistent, all searchable, all annotated with the operational consequences of upgrading.