Results from testing it anyway;
I have been using GB Studio for near 7 years, and just happen to exclusively use v1.2 due to later changes that overly complicated certain things. Ooh, this seemed so ideal for me...
I tried this with the source from my first fully developed, tested, and released game.
Built in GB mode. Failed to build in SNES mode.
So to be fair, I then tried the other four fully developed, tested and released games.
Built in GB mode. Failed to build in SNES mode.
Hm. AI scoring 0/5 so far here. Okay, let's try the four little simple projects I have sitting. Some one screen, up to six.
Care to guess the result?
That's nine out of nine projects varying from single screen demos to a six screen prototype that all built fine in GB mode, and failed to build for SNES.
0/9.
Needs a bit of work there. Perhaps a human will do it better.