Originally Posted by colby
I had this happen to me once. The gate agent couldn't use her scan gun on my ticket so she just keyed in the seat number (I was one of the first people on). Near half-way through boarding the real seat holder asked me to get up, and turns out I had a boarding pass from a few weeks earlier, for a different flight number (BP was for ONT, while I was on a LAX bound flight).
This happened to me about a month ago on a flight from SFO to LAX. The other person was ticketed on a different flight to LA. After we all flopped around a little bit and the other passenger left to get on her real" flight, the FA's repeated at least three times the flight number.