I watched the bidding on this hand in a recent GNT Open game. North opened 1nt and at one table it went 1nt-2d-2h-3c-3h-4nt-5h-7h ! The other table stopped in 6nt, auction unknown.
After I saw this hand, I immediately wrote to my partner reminding him of the need to play six-key RKC whenever a two-suiter faces a strong balanced opening such as 1nt/2nt. With that agreement, the bidding could go
1nt-2d
2h-3c
3h-3s
4c-4d (RKC, as responder is interested in a major-minor two suiter in which case the immediate suit after the minor is the kickback suit, when unambiguous),
4s(1430 structure, 3 keys out of 6), 4nt (Q-ask)
5c (no Q), 5nt(Specific King Ask, 5s can be Specific Suit Ask by agreement)
6s(Spade king)
So now, you have extracted as much information as you possibly can (if you had used SSA in spades you could have found out if pd had Kx of the suit or longer which could have been critical had you been interested in 7c, which could have been the case had partner shown the QofC and you suspected he had four of 'em; 7c would then be safer than 7h without the Jack of hearts, but that's academic now). You know pd has Kxx of hearts, AofD, KofC, but no Q and KofS. He must either have the Queen of Spades or two jacks for a minimum opener. Do you have enough info to try 7nt now ?
If you had discovered that partner was missing either the King of clubs or hearts, it appears to be poor grand, which would be the case if pd had something like KJx KJx AJX Qxxx or some unappetizing variant thereof, so it looks as though introducing clubs would have helped to some extent.

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