If you know from the bidding that East holds at least 5 diamonds, but you don know anything about what West holds, then you can think of East having 8 "vacant places" that could be the ace of spades, and West having 13.
If you know from the bidding that East holds at least 5 diamonds, but you don know anything about what West holds, then you can think of East having 8 "vacant places" that could be the ace of spades, and West having 13.