There was a bump out, but I don’t think it physically stopped you from putting the cartridge into the console, I don’t have a GameBoy on me to check right now though. You’re right about the missing notch though, but that would only stop you from starting it on the original Gameboy and not the Gameboy Pocket or Super Gameboy. I know for sure I saw the Pokemon Crystal error screen when I tried to play it on the wrong device after being able to play Pokemon Gold on the older hardware.