WARNING: High mycroftese here (i.e. long, complicated, potentially leaving you more confused than before). But also note that *a lot* of digressions have been ignored - this could be pages longer yet. Believe it! and thank your local Director, who has to actually understand this.
You are entitled to (what you can remember of) your system, the bids and plays made at the table, and the *agreed* meaning of calls made by your opponents. Almost anything else you get - from any source - is extraneous, and if it's from partner, it's unauthorized (*).
You may not make calls [ed: demonstrably] suggested by unauthorized information, although you may be required to use it in other cases (**). If North should have taken another call after the "correct" (to his mind) explanation and a 2
♥ call from partner (which should say "I don't care what your suit is, I want to play hearts!"), and didn't, then we may adjust the score (12C) based on use of Unauthorized Information (16C). But the OP isn't asking about that - and many players and directors forget to look. One of mycroft's axioms: "All misinformation cases are unauthorized information cases."
Explaining the reasons for pescetom's questions:
- "What is the EW agreement about X of 2C showing majors?" and "Had 2C been single suited, what would have been the meanings of Pass, XX, 2D and 2H after the X?" We need to know their agreement (and if there is significant difference between the double of a Landy 2♣ and a "one-suited" 2♣) to understand how hard it would be to find their spade fit. If after "one-suited", if double is still "cards", double of 2♥ passed is takeout, it might get there; but if it's Stayman, then it might be easier.
- "Did N do anything that might suggest he was uncomfortable with the explanation of 2C or the bid of 2H?" If so, then South also has unauthorized information that North might have forgot, which might influence his call(s). It might turn out that 2♠ by E-W would have been doubled by South looking at his 3 spades and partner's 4, and we're awarding +lots70 rather than +x20.
- "What demonstrates that the agreement was Multilandy?" This is the big one. The Laws differentiate between forgets and misexplanations, and between deliberately and accidentally violating system. If South's explanation is their correct agreement, and they have evidence pointing to that overcoming any evidence that it's single-suited, then North misbid. If not, then South misexplained their agreement.
Now, the answer to that last question (which is something the director must determine) determines the answers to the OP's questions. The main law dealing with this is Law 75, "MISTAKEN EXPLANATION OR MISTAKEN CALL"
If their agreement is actually Multi-Landy, then North misbid, and:
- "Is N supposed to inform opponents about the mistake after the bidding, before the lead?" No (75C). The oppponents are entitled to the N-S agreement, which they have correctly received. As a result:
- "Are opponents allowed to correct their bids?" No, there was no infraction. In fact, unless the regulatory authority has disallowed it (40B2a5), there would be no infraction if North looked at his single-suited heart hand and decided, deliberately, to bid it as "both majors". It's a psychic call, and provided South is no less surprised than E-W, psychics are legal (40C1).
- "If N's mistake is revealed as he puts down dummy, and opponents call director (claiming they had 4S), what is the correct ruling, and what is the relevant law?" "You were given the correct explanation as to their agreement, score stands." (75C again)
Now, if their agreement is that 2
♣ is single-suited, then South misexplained, and:
- "Is N supposed to inform opponents about the mistake after the bidding, before the lead?" Yes, as he is going to be dummy (75B3) (***). Again, the opponents are entitled to the N-S agreement, but this time they have not correctly received it. As a result:
- "Are opponents allowed to correct their bids?" No, with the exception of the last pass by their side (21B1a). However, the director should take arguments (in the ACBL, away from the table before play; other RAs have different strategies, but in all cases, no information should be allowed to be passed between defenders until after a result is determined) about differences in the auction with the correct information. Here's where Pescetom's questions about E-W's defences are also asked by the director.
After the hand, the director should explain what they have been told about E-W's agreements and desired actions, and with that and their own judgement (and those of who they consult with), determine the likely contract(s) with the correct explanation. If those would lead to a better score for E-W than that achieved at the table, the director shall award that score instead (21B3 leading to 12C. I'm not going into details of what score to assign, as this is getting way too long already. and that truly is in the weeds of Director Sorcery).
- "If N's mistake is revealed as he puts down dummy, and opponents call director (claiming they had 4S), what is the correct ruling, and what is the relevant law?" "You were misinformed, and North failed to correct the explanation before the opening lead. We can't take the auction back, but we will discuss alternative actions, and potentially a different opening lead. Play the hand as is, however, and call me back if you believe you were damaged." Note: the director should use their judgement (and that of those they consult with) independently of the damaged side; if they believe E-W were damaged, they should adjust even if E-W do not call them back. (21B3 again, but more so, 75B3 and other sections, all leading to 12C again)
(There's a third case, which comes up very rarely, but it does come up. If South realizes during the auction that they actually play 2
♣ as "one-suit" rather than "majors", then they must call the director and correct the information no later than the end of the auction (immediately on realizing is better) (75B2). The same thing as above happens; the last call by E-W can be replaced, previous calls affected by the misinformation will be analyzed for an adjusted score,...)
Now, not everything can be unambiguously determined on one side of the barrier or the other. The director has to keep several Laws in mind as they determine which of those two categories apply:
- Law 21B1b: "The Director is to presume Mistaken Explanation rather than Mistaken Call in the absence of evidence to the contrary." This means that if North's card says "one-suited" and South's says "both majors", or somehow otherwise the Director has doubts as to whether their agreement actually is what South said, they should rule Mistaken Explanation.
- Law 75D "Director's Determination". Several statements in here apply:
- 75D2: "It is a condition of any partnership agreement that both players possess the same mutual understanding, and it is an infraction to describe an agreement where the same mutual understanding does not exist." If it's written on page 63 of the notes that were changed Wednesday by South and passed to North Thursday, and this is the Friday game and North didn't notice the change, they don't have the "new" agreement. Same could apply to "yeah, we changed it last week, but I forgot".
- 75D3: "If the Director determines that the call has no agreed meaning, an adjusted score is awarded based upon the likely outcome had the opponents been so informed." This applies to "South said it was Multi-Landy, but they actually didn't discuss it and South (mis-)guessed", and also to "We play M-L, but we switched from Cappelletti last month and partner has forgot more than once" and other "actual agreements". Note that here, the director determines their actual agreement (e.g. "We don't have an agreement against 12-14 NT, but 15-17 it's M-L", or "We switched to M-L last week, but used to play Capp", or...), and rules based on how the auction likely would have gone had that been explained at the time, not automatically "I can't prove it's M-L unambiguously, therefore you should have been told 'one-suit'."
Yes, it's a common situation; one of the three most common "judgement rulings" situations in the game (the other two being "equity" revokes and "faulty" claims). None of these (nor any other judgement rulings) are simple; some are top-tier complicated. Some even do not have solutions that are unequivocally correct. Some are too complicated for a regular club director to get even close to right - but they can get 90% there, 90% of the time, with care and interest, and frankly, that's good enough for a director with good social skills to keep the game moving, the players happy(ish), and coming back. But they all boil down to:
- What is their actual agreement? Were the opponents misinformed, or did the player just misbid?
- If they were misinformed, can we fix the auction, or do we have to do an adjustment (or both)?
- If they were misinformed, was the misinformation corrected at the right time, or does that need to be looked at during the adjustment as well?
- IMPORTANT: were the non-offending side damaged? If 3♥x goes for 800, it doesn't matter that 4♠ makes, does it?
(*) One of the rare exceptions is that you can use *any* information you receive, including statements of partner, to realize that the call you put on the table is not the call you intended to make (Law 25A). But that's not a change of mind.
(**) For instance, if you are woken up to your system by partner's Alert or explanation, you must explain partner's calls according to your actual system, even if you must also bid as it would mean in the system you thought you were playing when you made your call.
(***) If they were defending, say 3
♠ by East, then North would have to remain silent until the end of the hand, so as to not aid South's defence. This is important to know, and another common source of Unauthorized Information. But this post is too long as it is, so I'm not going to go into it. Just know L73C/L16 leading to L12 if UI was "used".
[Note: I have to go learn about responses to 2
♣ and 2
♦. Will review this later and there may be minor edits. M]
When I go to sea, don't fear for me, Fear For The Storm -- Birdie and the Swansong (tSCoSI)