I found this today at a thrift store. The cartridge itself doesn't seem any different from the released version, but I'm going to open it up and check soon. It feels a bit heavier.
The box, though, has two 'Not For Resale' stickers on it, one on each end, covering the openings. Wasn't the Super Gameboy packaged in a larger-sized box, similar to Earthbound and Mario Paint? This box is normal sized, just like every other SNES box.
Was the Super Gameboy ever a pack-in with the SNES? Did it come in its own box?