undertale is well known for having generally messy coding.
many have noticed in particular that it's soundtrack on streaming services and the soundtrack in the actual game has some differences,
though most only know about death by glamour, strangely enough.
toby's way of coding his music is using something called "caster", specifically the code global.batmusic = caster_load("music/song.ogg"),
then using the code caster_loop global.batmusic, volume, speed).
"batmusic" is just what this flag is called in the battlegroup code, but is changed in other places to fit that context.
or sometimes he uses "global.dongus".
anyway, toby sometimes composes his songs at a different speed but uses some code in the game to change what speed that song plays,
probably so he doesn't have to edit his FLP's all the time when they don't fit a scenario. or sometimes he just does it for fun i guess, i don't know.
sometimes it's a case of dynamic music, changing a song in the game to fit the current mood.
and a lot of times the streaming service versions have differences for some reason too! it's all so strange, i don't know why he does it.
regardless, you can check out this playlist i made documenting all of the songs that have differences from the streaming service versions. i worked hard on this!!