meantime – does a “full scan” in firefly *purge* from Songs.db stuff which it can no longer find on disk? Or would I be better songs.db by hand (either see if I can remember enough SQL to create a suitable delete statement or just delete the lot and let a Scan re-build the list)?
A full scan does indeed delete everything from the database and start from scratch. Although, a regular scan would recognize that the songs were gone and delete them from the database, so either would work. Really, the difference is whether you want to force it to update the song metadata.
A regular scan will just update any changed files, and remove any deleted files. But a full scan will update ALL files.