Originally Posted by
Freyt
To loosely quote one of the devs of FFXV before the launch of the game, when asked if they could put in old FF music to listen to in the in-game car: "we own that music, and that sounds like a good idea, so we'll do that". And thusly so, a wide range of music spanning FFI - FFXIV was included in the game. Indeed, Square also owns the majority of the music within FFXIV. Not the intro title music that they commissioned from Uematsu, but all of the music created by the sound team under Square.