Old EpiDoc projects (pre 2010) still have XML that validates to version 5 or earlier of the EpiDoc DTD, which could previously be found at: http://www.stoa.org/epidoc/dtd/5/tei-epidoc.dtd (dead link).
These files must still exist in SVN (but maybe not in Git?). I suspect it would be a good idea to archive at least a couple of the most stable versions of the old DTD in the schema list at https://epidoc.stoa.org/schema/
Where would we need to put them to make this happen? Do we need to make a decision which version to keep/archive?