If you watch SWEGTA's videos you may've seen he made a video about the music thing:
Nate,an unused ped that is on the game files(I believe) was meant to sell you music according to the game sound files,but this was meant to be for the XBox Classic Canis Canem version,whose was never released.
Well,from what I read about the Beta School(or at least what I remember) is:
-Boys Dorm was meant to have 2 floors rather than just one,like Girls Dorm(Which makes more sense as long as there are much more boy students than girls),it even had a bathroom.
-There was an (it's still there but now is out of order) Elevator that connected the School's Roof and the Basement(Specifically the broken elevator found in The Hole),actually,when you start the mission"Russell in the Hole"(not "Help Gary" you may notice that the Clique Leaders spawn near the Elevator,making a reference they were meant to go and watch the fight by it=
-It was planned that the classrooms were gonna be enterable,but that idea was scrapped due to PS2 capabilities.
-(this one I don't remember if it's true but I'll say it anyways) You were able to get inside Principal's office rather than just the Reception (The place is enterable by modding,like the classrooms,but you'll find some collision errors and many bugs like Crabblesnitch's desk)
-I think the Swimming Pool was at some point refilled(although I'm not sure)
-Also,(this is more about the map in general) there were some Subterranean ducts where you could freely go around(again,PS2 limits)
-Mr.Luntz(Janitor),was mean't to spawn on the Basement
Well,I remembered a few of them,then,I had to watch SWEGTA's video to refresh myself a bit...Here
Bully BETA : The Map [EPISODE 2]