Here's another datapoint for you: I was on ORD/NRT back in September when some messy weather was causing bad delays in ORD. I was the last pax on the plane (delayed already by an hour or so) and they closed the gate and retracted the airbridge. Pilot said we would wait a couple of minutes for taxi clearance. Then the jetbridge comes back out and the gate attendant starts knocking on the door! I called over a FA to point it out, and then they start to open the door. Fortunately, just in time they realized the door was armed and stopped before the slide triggered.

Anyhow: they bascially boarded 4 more pax before closing up again, for good this time.