Programs can search you by name, AAMC #, etc. Might as well put it on there now. If you're feeling especially neurotic you can email the PC your NRMP number but they probably already found you.
I was recently contacted by a program coordinator because she was having trouble finding me on NRMP. It ended up being a mistake and she had been typing the number in wrong or something. I'd imagine anywhere that's ranking you to match will reach out to you if they have trouble finding you. So, nbd, they probably just searched your AAMC ID.