
Law 42A3 says dummy "plays the cards of the dummy as declarer’s agent as directed and ensures that dummy follows suit (see Law 45F if dummy suggests a play)."
Law 45F says "After dummy’s hand is faced, dummy may not touch or indicate any card (except for purpose of arrangement) without instruction from declarer. If he does so the Director should be summoned forthwith and informed of the action. Play continues. At the end of the play the Director shall award an adjusted score if he considers dummy suggested a play to declarer and the defenders were damaged by the play suggested."
Law 46A says there's only one proper way to designate a card from dummy. "When calling for a card to be played from dummy declarer should clearly state both the suit and the rank of the desired card."
Law 46B tells us how to interpret declarer's incorrect (because it doesn't follow Law 46A) call for a card from dummy.
It seems that it is incumbent on players either to be thoroughly familiar with the provisions of Law 46B, or to call the director every time declarer fails to follow Law 46A. I don't think we need to get into a long discussion of the objections to the latter. Or even a short discussion. That leaves us with the former.
When declarer's irregularity clearly meets one or the other of the provisions of Law 46B, I trust no one (except possibly the Secretary Bird) will object if dummy acts on his interpretation. What should happen if dummy doesn't understand what declarer wants? Can he ask for clarification without violating Law 43A1{b} ("Dummy may not call attention to an irregularity during play")? Can he sit still, saying nothing? If he can't do either of these things, what is he to do? Can he call the director, not to point out an irregularity, but to ask what he should do?
If he can't act, and he can't not act, he's pretty much screwed. Is this a (long overlooked) fatal flaw in the laws?