You are called to the table at the end of the auction, and again at the end of the hand.
The partnership play 2C non promissory Stayman. This is the method the partnership uses to make an invitational raise to 2N (even if they have no 4-card major) as 2N would be a transfer to diamonds.
The partnership agreement is that 1N - 2C - 2H - 3N will show game values AND 4-card S suit. With game values and NO 4-card major responder would just raise 1N to 3N.
North converted 3N to 4S as per agreement.
South now has a moment of panic, and bids 5C.
Everyone passes and you are called to the table, to review the auction, and again at the end of the hand.
South explains she'd forgotten the sequence to 3N showed 4-card S suit. She had decided to bid 2C en route to 3N "because I wanted to find out if my partner had got something in the majors".
4S does not look like a successful spot to South, and so she bid 5C over 4S.
3N makes, 5C is minus one, but 4S is worse spot!
NS got a bad score on the board.
Do you rule the result stands, or do you rule back to 4S minus more than one? Or something else?