Originally Posted by
CPRich
Fwiw, the pilot on my DXB-JFK flight on Saturday, after introducing himself and his co-pilot, announced that "because it's an extra-long flight, we have an extra crew with us" and introduced them - pilot and co-pilot. That's a verbatim quote, I wrote it down.
I did not try to correct him.

That happens quite often actually... but I think it sounds better to the average pax, instead of trying to complicate things by saying 'we are crew A who will fly the aircraft for the first hour or so... then we will switch to crew B so we have our designated rest... blah blah blah'.
However it definitely wouldn't be correct if they are flying DXB-SEA and have 4 additional crew who are actually deadheading all the way to SEA... which commonly happens for picking up new airplanes and such from PAE.