I thought I heard that ANY plane the president flies on is considered “Air Force One”. That there doesn’t necessarily need to be any specifically designated Air Force One.
Only if it’s provided by the Air Force. It’s also important to remember that Air Force One is only Air Force One if the president is on board, it has a different designation otherwise. Which became logistically interesting when Nixon resigned, technically he was president until Ford was sworn, but he went straight onto AF1 and was flying to CA when that happened, so the plane changed designation in flight.