The additional sad fact is that AS agents used to simply add a tag to the existing reservation (for the additonal flight) and reissue the ticket. Now, most of them will just rebook you if the entire itinerary is available as a new reservation, which typically occurs on or about the twelfth of never. Unless I'm rebooking with an agent on the phone, I'd rather eat $12.50 than risk the unfortunate experience of the OP.