Originally Posted by FliesWay2Much
Same thing happened to me a couple of weeks ago in HSV. The WX and a broken airplane combined with Friday PM DL overbooking caused them to book me on a NW codeshare through MEM. Sure enough, the SSSS printed out on the NW boarding pass. I kicked myself for not printing out Spiff's tried & true rules for defeating the SSSS. The funny thing was that the NW gate agent didn't seem to care. No band of roving screeners showed up at the gate, although I already had finalized my game plan -- making them change gloves, etc. I held my thumb over the SSSS when I gave the boarding pass to the gate agent and I boarded unharassed. I don't know why.
(Oops -- fixed a typo.)
If a person isn't a selectee and changes flights at the gate they shouldn't be made a selectee. This is a problem with the system. As stated, the GA or TA can deselect you for this reason but most don't want to be bothered.