Misinformation
Bidding opened 1D, LHO overcalled 3H, responder (S) asked and was told bid was strong, he then passed and RHO raised to 4H which became contract. Prior to opening lead LHO corrected the information as the bid is pre-emptive in their system. Responder then called me (playing director) because he might have made a bid had he known the bid was weak.
I reviewed the hand at the end of the session. I think most responders would have bid 3N, 4D or 5D, RHO would likely have bid 4H even if he knew the bid was weak and certainly would have believing it strong. Should I adjust score - at the review I felt the outcome was marginal and let the score 4H - 2 stand.
North: S KJxx; H -; D AQJTxxx; C Kx
East: S xx; H QTxxxxx; D xx; C Ax
South: S xx; H Axx; D Kxx; C QJTxx
West: S AQTxx H Kxx; D x; C xxxx
Comments
S is quite likely to bid something with the correct information. 5D seems like a bit much for me (especially because S wasn't certain about bidding at all, and 5D is a very optimistic bid with that heart holding); 3NT is probably most likely.
I think there's a decent possibility that West, thinking that East is strong, makes a penalty double (East, with UI suggesting running, can't run from this due to the possibility that West can run a suit to defeat the contract). This seems like the sort of situation that calls for a weighted score, and I think I'd include proportions for 3NTX+2, 4H-2, and 5D= (5D is reached after 1D, (3H), 3NT, (4H), 4S, 5D).
There is also the possibility that 4H would have been doubled (on points - South isn't entitled to know EW are having a bidding misunderstanding but can work out the points may be evenly distributed). Which is why polling is needed (an awful lot of it since West thinks the 3H bid is strong and East has UI that demonstrably suggests running if West takes any action over South's bid.).
There is also the problem with responder calling the director - since his partner now knows that he hasn't a weak hand but values enough to consider taking action over 3H (otherwise why would he be calling the TD?) - this is UI - and the reason why the side who has given the wrong explanation should call the TD before they correct it so the TD (as a NPTD) can take South away and discuss matter with him without generating the UI).
I think you need to be careful about judging for yourself what South would have done with the right information.
I would have taken a poll at the end of the session (it's a bit skewed as some will have played the hand, but if necessary I could have polled others away from the event),
Give various players of similar ability South's Hand and the auction as far as 1D - 3H (with correct explanation),
ask them what they would do and when they've told you that ask them whether they gave real consideration to any other action.
I think I'd also explore whether North would have bid 5D over 4H with the correct explanation. Although this depends a bit on the vulnerability I might have polled people with the North hand and the correct explanation after 1D - 3H - Pass - 4H - ?.
Personally I wouldn't have given much thought as South to raising what could only be a 4-card Diamond Suit.
I might have considered Passing if part of our agreement was expecting partner to at least re-open with a double.
Peter Bushby Suffolk
To me, the choices seem to be either 3NT or 4C, which partner could view as showing tolerance for diamonds. Passing is fairly low on the radar. Double is also an option, unless our agreements mark the bid as clearly punitive.
I'd also add 4Hx-2 to the list ais523 gave for weighted considerations.
If the 'outcome was marginal' the TD should err on the side of adjusting the score. In misinformation cases it is normally possible that one of the legal outcomes is the table result, so the TD can always adjust to a weighted score including some proportion of the table result.
I think the director should first offer South the chance to change their final pass under Law 21B1a now that the misinformation has come to light.
I suspect South might decide to double instead of pass at this stage.
Take a look at this recent thread, MR...
https://www.ebu.co.uk/forum/discussion/765/misinformation
Sorry, silly me, you were already in on that thread.
I think that, without the MI, after the sequence:
1 !d - 3 !h(weak) - pass - 4 !h
pass - pass - ?
South might decide to double
Is the LHO allowed to say that partner has given an incorrect explanation? The 2D5 in the Blue Book seems to say that the explanation should only be given after the hand has been played:
2 D 5 If a player believes that it is possible that partner has misalerted or given a wrong explanation, he must call the TD and explain the situation at the appropriate time (Law 75B):
(a) If he becomes declarer or dummy, before the opening lead is selected; but
(b) If he becomes a defender, at the end of the hand, not earlier.
LHO was declarer given the bidding so far, so before the opening lead is the correct time to make the correction. (As your quote mentions, a defender would have to wait.)