No alert
x J109xx KQJxxx K in 4th seat
1C - P - 1S - 2NT (not alerted)
P - 3NT - P - 4D passed out
4D scores better than 3NT
Having reserved rights at the time opponents ask for a ruling ?
1C - P - 1S - 2NT (not alerted)
P - 3NT - P - 4D passed out
4D scores better than 3NT
Having reserved rights at the time opponents ask for a ruling ?
Comments
There are two issues here, unauthorised information and misinformation. You haven't posted enough information to be able to handle the misinformation parts of the case, but let's assume 1st and 3rd seats would have passed over 2NT/3NT respectively either way. (You'd need to see their hands to know whether they would, say, consider competing if they knew that 4th hand was short in their suits.)
The 3NT bidder has no unauthorised information, and thus hasn't committed any UI issues (although they've given misinformation to their opponent). So the only potentially offending bid from a UI point of view is 4!d.
To be legal, the bid has to fit into one of three categories: made when no unauthorised information exists (clearly not the case here); the only logical alternative in the situation; or an alternative that is not demonstrably suggested by the unauthorised information.
From 4th seat's point of view, the 3NT bid would be fairly surprising if it were alerted properly. One thing that has to be established is whether there's a partnership agreement about 3NT over 2NT. (I'm assuming that 2NT, for this partnership, is an "unusual notrump" meaning 5-5 in diamonds and hearts). If it's "no preference" (possible but unlikely), there's clearly no logical alternative to pulling to 4!d, so the bid would be legal. Likewise, if playing "all strange bids are forcing" (a known meta-convention), 3NT (a strange bid) would be forcing, the only reasonable replies to it are 4!d and 5!d, and the unauthorised information (which suggests that 2nd hand is strong) would favour 5!d over 4!d, thus 4!d is the only legal bid.
If there's no agreement about what 3NT means and no useful meta-agreement, I'd assume it'd be natural / "to play". 4th seat's hand is not very different from what their previous bid shows, so once their partner makes a bid to play, I as 4th seat would pass it (in a hypothetical auction where no unauthorised information exists). Typically speaking it's worth asking a range of players of the same strength of the players to determine whether a bid is a logical alternative or not, though. If pass over 3NT is a logical alternative (and at least on my bridge judgement it is), then 4!d is clearly illegal: unauthorised information (the non-alert) exists, another alternative (pass) exists, and 4!d is suggested over pass by the unauthorised information (because the non-alert implies that 2nd hand believes 4th hand has club and spade stops, and thus makes it quite likely that at least one of these stops are missing, making it more attractive to run from a notrump contract).
If the 4!d bid is disallowed, it needs to be replaced with the legal bid that would likely have been made instead. You can give a weighted verdict here in some cases, but here you don't need to; I think the only other likely bid is Pass (you could make an argument for 5!d but I don't think it's a good argument). Assuming 1st hand would pass that out, you should give the score that would be achieved in 3NT. (Again, you can give a weighted verdict here if you're unsure what the score would be.)
I'm not sure that it is sound to apply a meta-agreement that "all strange bids are forcing" to 3NT bids. I prefer "3NT ends all auctions" or the less extreme "3NT is to play if you have what you have shown".
Besides, why is 3NT strange? Why cannot the 3NT bidder (particularly in these days of light openings and responses) have a balanced hand with some black suit stops and a red suit filler or two? Even if he has a hand where he should be thinking of passing 2NT, he may bid 3 on the basis that 2NT will rarely make precisely 8 tricks so it is better to go for the option with the biggest upside.
In that context I would take a lot of persuading that passing 3NT was not a LA. Having six good diamonds and five bad hearts is positively good for the chances of 3NT opposite the type of hand which I have postulated. If partner alerted, explained as the reds, and bid 3NT, would we all not pass happily?
This looks like a routine UI adjustment to me unless the players tell me anything unexpected.
Clearly the players are thinking in terms of a UI adjustment. Of course as TD you should always consider MI as well, and vice-versa, but I agree that we don't have enough information to look at MI in detail.
9 J109xx KQJxxx K
which may be AB's 6 good diamonds
Anyway, the director (at an EBU affiliated club) ruled "he's entitled to bid his hand" so 4D is ok.
If it makes any difference ? the pair have played about twice a month for years and are NGS approx 57%.
He's entitled to bid his hand, but not twice.