Once you get 'selected', you are labelled for that flight.
I was at LGA on AA and had the tap on the shoulder. So off come the shoes and out come the electrical devices. After we boarded the aircraft, we were asked to leave due to a malfunctioning lav.
We then boarded a second aircraft and I was checked again. Had to leave that Fokker because of presurization problems.
Upon boarding the third aircraft...you guessed it.
Next time I'm wearing slip-ons.