What's the contract?
Playing with screens.
North, who will be declarer in NT, bids 4NT (natural and invitational)
Tray passed under the screen
South considers matters for a while, and eventually bids 6NT
South and West, distracted by South's time spent thinking, do not immediately pass the tray under the screen but instead remove all their bidding cards from the tray. It is then pushed back with their side empty. North and East assume that 4NT has been passed out.
Note that technically the tray is supposed to be passed back showing the final passes before the cards are removed, although that very rarely actually happens. Thus all four players, and certainly both South and West i.e. both partnerships, are offending.
North and East play and score the hand assuming the contract is 4NT. South and West do the same assuming it is 6NT. As South was looking after the bridgemate, it is in the official result as being played in 6NT. The discrepancy is not noticed until after the end of the session (in the case of EW, until they were in the car on the way home; I don't know when NS realised). The correction period has not expired as there is another day to the event.
How do you rule?
In this particular case, it didn't affect either the play or the defence (although declarer might have taken longer over the play if he thought he was in 6NT). Does that matter?