That is not how copyright works with music. There are separate copyrights for written the music (the rights to reproduction of the song) and a particular record

That is not how copyright works with music. There are separate copyrights for written the music (the rights to reproduction of the song) and a particular recording of the song. If I write a song I own the rights to that song. If I allow Taylor Swift to record it, she owns the rights to her recording of it. She controls how that recording is reproduced, but I can still allow other people to make their own recordings. So, even though the rights for Bach songs have passed into the public domain, the people who make recording still own the rights to their recordings of the song, just not to the song itself.