I have no clue actually- the email specifically said that I had been accepted/waitlisted at a school that participates in the AAMC certipho background check program. I haven't been accepted by any other AMCAS schools because I withdrew from all of them except 2, which I'm waiting to hear post interview from both. So I have no idea if they have to request for your consent every time a new school accepts/waitlists you or if they do it just the first time.
I'm pretty sure you only get that email once.