I’m pretty sure I’ve had the MMR vaccine more than once. Probably got it as a kid to get into school. Definitely needed it to get into college, but didn’t have records to show I already had it, so they just gave it to me again. Then got all kinds of shots in the military. Wouldn’t be surprised if yet another round of MMR was one of them. Point being, just tell the pharmacist that you don’t know if you already had it, but wonder if it’s safe to just get it again. They’ll probably answer, “Which arm?” 😉