I don't know the official policy on this (must be security sensitive info ) but the only time I've ever seen anyone deselected from haraSSSSment is when they've been involuntarily rerouted from one airline onto another, provided they were not a selectee on their original flight. A while back at CHO, a United Express flight to IAD was cancelled (as happens all the time) and UA rebooked some of the passengers onto my US Airways flight to CLT. I noticed that the ticket agent had stamped a big red "EXEMPT" over the SSSS---a good idea since CHO has only one metal detector and three or four screeners on duty at a time, and 20 SSSS's would have taken forever to process.

There's no valid reason for SSSSing anyone in cases like this; the passenger profiling system needs to take into account that last-minute one-ways, or any other type of ticket, are not "suspicious."