The other MIDIs have been renamed somewhat.
In-game, the MIDIs don't play. Rather, the CD audio of the registered version is supported. I mounted the SW CD and it played the end-of-level screen music (track 2) for the first level rather than the track used in the final (track 3). Unfortunately, this beta was not distributed with CD audio, so we can't know what the CD tracks sounded like at that point.