What's more, they provided several months' notice of what was going to happen, how, and when. That gave people who had AmEx Membership Reward points and wanted AA miles (a move that is generally not possible, except via a series of program transfers with substantial loss of value) a chance to move them into TWA's program and have them become AA miles in due course.

When AA bought a smaller Western airline previously (Reno Air?) it was handled similarly. In this case the advance notice gave people time to sign up for Reno's program, which had a sign-up bonus, and have that bonus become AA miles without ever even seeing a Reno (or whatever it was) plane.