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.