The irony is that this very same month I have released a new book called "Variable Key Card Blackwood" where this problem is solved. [Through Master Point Press (see http://ebooksbridge....products_id=521 for the ebook; paperback will available very soon also).]
With VKCB (actually MKCB or "Middle" Key Card Blackwood), the auction would be:
(1♠)-X-(P)-4♥
(P)-4♠(kickback MKCB)-(P)-4NT(2 key cards)-P-
(P)-5♣(clarification ask)-(P)-5♦(no trump Queen, no trump King, hence two Aces)
(P)-7♥
Had Advancer held the trump King and thus only one Ace:
(1♠)-X-(P)-4♥
(P)-4♠(kickback MKCB)-(P)-4NT(2 key cards)-P-
(P)-5♣(clarification ask)-(P)-5♥(no trump Queen, trump King, hence one Ace)
(P)-6♥
What if Doubler did not have the trump Queen (E.g., ♠AQ ♥AJ10x ♦KQ109xx ♣x)? Opposite one Ace and the trump King, the small slam makes if Opener has the trump Queen, a fair bet, and makes easily if partner has it. If partner has two Aces, the trump suit probably comes in on a double hook. Thus, you expect to bid the small slam any time partner has two key cards. To make a grand, however, you want partner to have specifically two Aces and the trump Queen. That grand can also be found with VKCB:
(1♠)-X-(P)-4♥
(P)-4♠(kickback MKCB)-(P)-4NT(2 key cards)-P-
(P)-5♦(asks if partner has specifically two Aces and the trump Queen)...
Rather ironic that Auguest Boehm would note this issue in December of 2012.
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