It's no big deal, but MJ says the cartridge he took home with him is not his. Also, he doesn't have his own cartridge.
The cartridge he has now has a sticker with the word 'topy' on it.
MJs cartridge is (most likely) Dutch, so it might say NL somewhere in the fine print on the back or something. Also all his times are on it, such as 59"99 on MC1. He hasn't marked his cartridge though. That kind of also narrows it down in a way as most people have marked theirs.