I'm afraid that is untrue. For example, let's say you have booked a s/p/d package, then FD is released, and the time during your stay qualifies. There are a set number of blocks of rooms at select resorts that Disney deems qualify for FD. Once that block is filled, the game is over. Under your theory, a guest would not need to worry about that block filling up if Disney merely needed to add the promo to your account. In reality, they have to cancel the reservation and place you in an open "block" of FD promo-qualifying spaces.