The link to the past tileset's i'm using (Which is from Solarus' site) seem to function. but they aren't appearing in the dropdown box on the "Tileset" Box. neither do they have the symbol that indicates they are.
Attached to this post are two images. one is of blue.dat, the other of overworld.dat, which is here for comparison sake. overworld's tile set (and by extension house and castle) all work, meanwhile, blue.dat and the other tilesets do not. I can only assume that the Incorrect, none spaced text is the origin, possibly making it so that the file is unreadable to the program. I, however, felt it was best to contact professionals before trying something that drastic.
RESOLVED!
Thank you PhoenixII54 for your help!