It could very well be an undumped revision. The old Nintendo games are difficult to sort out. They often used a red stamp (letter and sometimes letter and number) for revisions and regions which sometimes faded off completely and people don't think to check them and the boards are too expensive to just buy them up to check. Some I've bought and have ended up matching dumped sets even when having a different stamp. So it's a really expensive crapshoot basically.