Some info on how they were lost

Lucasfilm allegedly sent the original master tapes to third-party mixers to make the 12" club single of "Lapti Nek." Long story short, they never got the the tapes back. Either the tapes got lost in the mail on the way back, they neglected to send them back (meaning somebody may still have them), or the worst possible scenario, they actually sliced up the masters to make their remixes. Total travesty! See here: https://originaltrilogy.com/topic/The-lost-song-from-Jabbas-palace/id/6174

Someone also alleges that "Galactic Dance Blast" was lost for the same reasons, though this time it was sent to PBS for the documentary From Star Wars to Jedi. There is some debate in the thread whether or not the story is true, the deniers using the NPR radio drama from 1996, which apparently has some of the music, as evidence.