At the charter terminal (#2) in Havana they can park 3 aircraft next to each other or up to 7 on the same ramp and frequently they board more then one flight at the same time.
Pax walk from the terminal to the aircraft ( 100 yards or so) and security personell at the bottom of the stairs check the boarding stubs.
Especially when flights are departing
to the same destination we had the Lead FA check stubs again while greeting.