Retail channel database schema versions that are reached by applying certain hotfixes were not supported for further upgrades. This hotfix resolves that, and allows customers on those versions to reach our latest and greatest releases!
Our channel database upgrade code generates upgrade scripts for Microsoft-provided schema by comparing a target schema to the database's current Microsoft-provided schema. Database versions too old to have a column storing their current schema rely on a file in our codebase to describe their current state.
Some such schemas did not have a file describing their state in our codebase. We added the necessary DACPAC files (files that describe a database's schema) to our codebase. This allows the database versions described by those DACPACs to be upgraded.