I was on a flight recently from SFO to LAX. At the same gate was a flight to PHX (or somewhere like that).

When we had all boarded, the FA's reported that there were 2 more PAX onboard than there should have been. They asked who was not going to LA and no-one answered.

So rather than stuff around, they just closed the doors and off to LAX we went. Quite uneventful really.