I would call up Princeton about the AP Eng test. It seems to me that if someone is not taking a test associated with a class, they should not have to take it - you could make that point, i.e., when he applied, he thought he would self study for it but other things got in the way. And if they say he doesn’t have to take it, I would backstop that by sending an email (i.e., just to confirm as discussed with [x], . . . ).