Oh! That makes sense, I kind of figured there should've been something there in the cluster for that. I'm not really all that rounded in that side of .wad editing so I mostly just kind of have to look up everything.
I'll fix it in a jiffy, then! Thank you both so much!
edit: Or uh, maybe not. I have the new "sky1" line in my MAPINFO but it doesn't appear to have done anything.
For example, this is really all I have at the moment.
map MAP01 "wip"
next MAP02
secretnext MAP02
sky1 = "SKY1", 0
cluster 1
music D_RUNNIN
map MAP02 "idk"
next EndGame
secretnext EndGame
cluster 1
music D_STALKS