Problems keep popping up. The problems are rarely discussed. You mess it up, or flail about, and maybe forget about it. Maybe you discuss it, but only after the bad result. Most problems can be resolved, however.
Here's a case in point. You open 2C strong, forcing, artificial. Partner bids 2D, artificial, GF, with at least one King or two Queens. You bid 2S. Partner bids 4S, showing a dead minimum with no controls (no Aces or Kings, no stiffs or voids). So, he has two Queens. How do you unwind the Queens?
The answer seems to be to bid 4NT. This cannot be ace-asking, as partner has already told you the answer. Partner is expected to bid Queens up-the-line. If he bids 5H, you will know that he has the heart Queen and the spade Queen.
If partner bids 5D, you know that he has the diamond Queen and either the spade Queen or the heart Queen, but which is his second Queen? If you bid 5H Last Train, is he supposed to go with the heart Queen? How can that be more important than the trump Queen? If you needed the trump Queen, how would you ask for that without inducing acceptance because of the heart Queen? It seems that Opener would bid the slam if he needed both red Queens, so 5H seems to ask if Opener's second Queen was the trump Queen, not the heart Queen.
If partner bids 5C, you know that partner has the club Queen and some other Queen. You can unwind this as well. If the club Queen and diamond Queen would work, bid 5D. If partner hears 5D and has the minor Queens or clubs and trumps, he bids slam. If partner hears the 5D call but has the club and heart Queens, he bids 5H. If you need the club Queen and the heart Queen, but not the diamond Queen, you bid 5H. Partner accept with the club Queen and either the heart Queen or the trump Queen. If you need the club Queen and the trump Queen, but not the diamond Queen or the heart Queen you are stuck.
If you need a specific Queen and the trump Queen, you bid the specific Queen that you need.
If you need both red Queens (the two directly below trumps), you bid 5S. Partner should go with both of these Queens, or with one of them and the trump Queen.
This seems to cover all situations. Note that the trump Queen is always deemed useful.
Now, suppose hearts are trumps. You do the same thing, except that you start with 4S. 4NT by Responder shows the spade Queen. 4NT by you asks for specifically the spade and heart Queens. 5H asks for the two-below Queens (club and diamond).
This same unwind should work whenever partner, for some reason, is known to have precisely two scattered cards.
Again, the structure of the unwind:
5M = Bid slam if have a card in the suit immediately below this and a card in the suit two below this, or either one and the trump Queen
5new = Bid slam with this card and the missing trump card
4NT = Bid slam with the spade card and the heart card (hearts trumps)
4M+1 = Bid Queens up-the-line
4M+1, 5M-2, 5M-1 = bid slam if you had the 5M-2 Queen and the trump Queen
4M+1, 5M-3, 5M-2 = bid slam with this Queen or the trump Queen, or show the next one
4M+1, 5M-3, 5M-1 = bid slam with this Queen or the trump Queen