This game has unused music.
Drift Out is the only game in the series to be played from an overhead, top-down view (apart from the SNES title Super Drift Out) and without any manufacturer licensing at all.
There are three unused songs in the game, all explicitly marked as "NOT USED" in the sound test menu (also used for IDs that do nothing there).
18 is an unknown, looping track.
1A is a tone that would have been likely used if the player opted not to continue or if the player wins a stage in the first place.
25 is an alternate ending theme.