Your sqlite query might give someone the impression that MediaID is duplicated when really what is shown is that of just one record in the group. MediaID is the Primary Key for that table and SQLite enforces it to be unique.
I’m surprised by the change reported by @thejerrybryan in filename duplication from RM7 to RM9. What surprises me is that there was any prevention of duplication in RM7 as I do not recall it and it certainly is not constrained in the table definition. I do not know when the application software imposed it. When captions were moved from the MediaLinkTable to the MultimediaTable in RM5, I made a pre-upgrade sqlite procedure that preserved the tag captions by using multiple records for the same Media File. It continued to be possible to add the same file and apply a different caption through RM6, iirc.
Edit: I went back to RM7 and RM5 and now know that the software constraint was added in RM5 and persisted through RM7 and still does in RM9 for drag’n’drop (added after RM5) but not for Add New Media. My query that converted multiple captions for the same file record in RM4 to multiple file records with unique captions (and distributed the tags accordingly) worked because there was no UNIQUE constraint on the path and filename as stored in the table. However, the RM5+ application software prevented further such replication of unique path/name combinations until RM9, which has loosened it up for Add New Media (probably unintentionally).