Whatever you do, do it quickly. Some programs have 30-day or 90-day limits for retroactive credit. The idea is that someone who flies with them and finds out about their program en route will be able to sign up and get credit for it, without having to interrupt their family vacation trip by rushing to a computer the instant they land, but to keep people from resurrecting that flight from 1997. (I know, a bit of an exaggeration because 1997 miles would most likely have expired absent any intervening activity, but that's the general idea.)