We're going to try to move up to the earlier CLT-BGI flight because it has 6 more F seats available than the PHL-BGI flight (assuming this holds true the morning of our flight).

Every time I've "moved up" I've been rebooked into a Y class ticket (each time times, F is sold out). Is it safe to assume that if F is available, that Y class will be immediately upgraded into a P class FC ticket? In other words, when I check in at BOS will I know if we'll be upgraded for our CLT flight immediately?