IDMUSxx cheat ded oversights
I'd imagine this is an oversight more than anything else and not a big thing really (especially given Dday's playmusic xxx command).
The IDMUSxx cheat always plays whatever lump the loaded audio def has for the map selected by the cheat. It ignores whether the music for the map has been changed in the loaded map def.
Also, related, the cheat seems to have a hardcoded range still. It can't read beyond the original game's 1-35 track numbers when there is more than 35 maps being loaded (i.e you can't type IDMUS36+) even if there are Maps36+ being loaded).