Duplicate rules, the opening of Law 13:
"When the Director determines that one or more pockets of the board contained an incorrect number of cards, *) and a player with an incorrect hand has made a call, then when the Director deems that the deal can be corrected and played normally with no change of call, the deal may be so played with the concurrence of all four players. Otherwise, the Director shall award an artificial adjusted score and may penalize an offender."
*)with the footnote being if three hands are correct, L14 applies instead. Doesn't apply here.
So, first the Director decides if the deal can be corrected. If it was dealt 14-12, even if it's the fourth round before it was noticed, sorry, it can't be corrected.
Assuming it could be corrected, the Director decides if it will play "normally" after correction.
If she does so believe, if any of the players disagree for any reason, or feel uncomfortable, or think they will get a better score assigned than if they play it, or just want to get to the bar earlier, they may say "sorry, I don't want to play this."
If you get through all of those steps, then play it out. I would suggest it isn't very likely if they're halfway through play...
So the director awards an Artificial assigned score, which would depend very strongly on how the 14-12 came about:
- Average Plus if a pair is completely not at fault;
- Average if a pair is partially at fault;
- Average Minus if the pair is directly at fault.
Note: I don't know about Ireland, but in the ACBL, we have a regulation stating that all contestants must count their cards face down before looking at them. I assume the IBU has something similar, in which case declarer and dummy are already "at least partially at fault", for not doing so.
Note 2: if it went 14-12 at a previous table, the people that caused this can be hit with a procedural penalty. If it was a normal accident, fine - "please be more careful in future?" If it was because somebody at a previous table pulled the two hands out after play to harangue partner for his play, then the penalty may be a little steeper...