Does PSA mark dirty cards as Altered (i.e. those dots at the back, which usually occur after a few years after handling the card by hand pretty often - I’ve had quite a few cards from my youth with dots like that)? You could try to clean those gently with a soft fabric before resubmitting perhaps?
EDIT: Coincidentally someone asked a similar question about those dots yesterday: www.elitefourum.com/t/black-spots-on-the-reverse-of-a-card/28205/1
Greetz,
Quuador