Originally Posted by
enpremiere
It is interesting that they posted shortly after the purchase rather than when the journey ended. All AA has to say on their official page is "In most cases, the AAdvantage miles you purchased will post before you arrive at your destination" but I had always assumed that you had to start your journey first.
Again, I think AA is happy to take the revenue here and, in the aggregate, would much rather have all mileage multiplier transactions be final, rather than reversing some -- even if (in cases like the OP's) there are occasions when AA would rather sell the miles at the regular lower rate but earn its transaction fee.
Mileage multiplier is like an impulse buy at the grocery checkout. Usually no good, but every now and then it could offer the best deal on a single York peppermint patty or whatever.