Just to add a few data points to the SNES dungeon crawler discussion:
As far as I can find with a bit of research, there are only a few unlicensed games that were released publicly for the SNES; a couple hentai games, some Chinese pirates, and Super 3D Noah's Ark. All but the last one are extremely obscure, at that (I didn't know there were any others at all until I looked on TCRF). So it's probably not a bootleg of some sort.
If it's not Eye of the Beholder or Dungeon Master and you aren't remembering wrong, then odds are high it'd be a prototype of some sort for a game that was never released. The character selection sounds a lot like Dungeon Master, which had 24 characters of which you got to choose 4.
Re: swapped labels: I had that happen once with a rental game, but it was a much weirder swap - someone had swapped Lufia 1 into a Breath of Fire 2 cart. I didn't actually get to play Lufia 1 either, because it would freeze after the intro.