Ok so after searching around a bit, I noticed Titenic's/Harry's Legend's music isn't exactly original and actually did come from the movie's soundtrack. The only thing is that the NES versions are faster then the original and slightly different.
Level 3/Select Screen of Harry's Legend and Track 4 of MK4's NSF is Rose's Theme:
http://www.youtube.com/watch?v=OSZCFFpix2gLevel music (other then Level 3) of Harry's Legend is the Titanic theme (Celine Dion - My Heart Will Go On), start at 0:20:
http://www.youtube.com/watch?v=saalGKY7ifUStill no idea where Harry's Legend's title screen music (definitely not from the Harry Potter film though) and boss music is from.
Also I tried identifying all the tracks in MK4 and this is what I came up with:
Track 1 - Superman Theme
Track 2 - MK3's select music
Track 3 - Kart Fighter (Unused)
Track 4 - Rose's Theme
Track 5 - Garou Densetsu Special's select music edited
Track 6 - The Bank from MK3 (done differently)
Track 7 -
Track 8 - Original, uses Track 6's triangle from Jing Ke Xin Zhaun though.
Track 9 -