Unless the mechanisms governing PAUSE uploads and indexing have changed, itís impossible to release an earlier version number than what is there already. So, if you had say v3.0.1 for a legacy version and want to release a bugfix v3.0.2 you cannot (formally/CPANally) do so if you have released new version v4.
A name change or a number in the name skirts the issue. Itís not unheard of even though itís a little clunky; e.g., LegacyXyz and LegacyXyx2.
Two versions sounds nice/kind and I appreciate your willingness to keep them up if you can work out how.