Taking a stab in the dark here, but one of them might be a bootleg. There were quite a few GBA games that were bootlegged around that time, and I ran into a couple myself. The only way I could tell the difference was that the plastic of the cart is a bit darker than a real GBA cart. You can't really see it well unless you have it in hand.
Of course, I could be wrong. Could just be a running change from the company.