West leads the 3. Dummy (north) goes down and 3 is there too! After investigation we find out that all four players have 13 cards, but the 6 is missing form deck.
What is our ruling? Which Law do we apply?
Law 1 is a good place to start!
Technically, the hand which should have S6 has the wrong number of cards, since S3 is surplus. Apply Law 13C tells the TD to remove the surplus S3 and then Law 13B2 tells us to award an artificial score because a call has been made on a hand which (it turns out) had the wrong number of cards. But nobody is offending, so the artificial score is AVE+/AVE+.
Of course if this is not the first round then you should investigate where the board came from. Just recently I have heard of a case where this happened on two different boards on the second round, obviously been mixed between the two boards in the first round. Goodness knows what the players in the first round were up to.
Law 1 is a very good place to start indeed!
Law 13C tells the TD to remove the surplus S3, but then if we start applying 13C, couldn't we continue by applying Law 14B - Missing card (Hand found deficient afterwards), instead of applying 13B ?
And if we are under law 14B, shouldn't the TD allow the completion of the play?
13B says about one player originally having more than 13, with and another fewer than 13. Is this our case? Or after removing the surplus, we just have one player with a missing card?
Law 1 is clear
If the board has two Spade 3s then bridge is not being played and the board should be cancelled.
If this board has already been played then White Book 2.8.2 f indicates that a procedural penalty should be applied to any pair who has "... passed on the wrong 13 cards".
Any player who has already played this board has passed on the wrong 13 cards.
Should the laws be applied blindly or should one take into account the fact that the cards involved, S3 and S6, are both small and would most likely not have made any difference to the calls that were made by the player who had the wrong card? If the hand can be allowed to be played by simply replacing the S3 with the S6 in the hand where the latter should have been and the TD determines that this would not have any impact on the result, consequently no damage to either side, let it go ahead. Allow West to change his lead without penalty if he was the one with the wrong card.
We are supposed to allow a normal result to be achieved as far as possible.
Application of Procedural Penalty to the pair that may have passed on the wrong cards is a separate issue.
As a practical matter, replacing dummy's S3 with S6 seems a way of letting everyone get on with the game. If there are objections then the TD may need to take a more formal approach to ruling on the board.