You know what's fascinating about that?

I'm pretty sure that every CD had the entire game and all the art assets for every town / place you could enter on the world map. Every enemy. All the music.

The only difference between each CD was the FMV cutscenes contained on them.

At least that was the story / rumor at the time. For optimization they could have reduced the art assets and music to only areas you could enter at that point in the game, and only enemy models you would see, but supposedly that wasn't the case.