This is a situation that came up a while back, but has recently come to mind.
North goes to get the next board from the previous table. When he picks it up he notices the East hand has been placed in the pocket upside down, and the Ace of Spades is clearly visible on the top.
He is flummoxed and goes back to his own table for advice (or possibly want of anything else to do) - the board surely cannot be played if he has seen part of East's hand.
Of course it can, but not now all four players have seen AS.
He should have called the director, but is it so bad he didn't?
What is the assigned score, and what procedural penalties should be given?
Can the board now be played? No.
Who is responsible? Certainly East at the previous table, but also North at this table - if North had called the director, there would not have been a problem.
So what is the assigned score: Is it NS 40, EW 60, because North is directly at fault (per WB 8.12.8, although this talks about actions not lack of actions)? This seems harsh, as North has committed no infraction, and previous East is also directly responsible.
Would NS 50, EW 60 be better? If so, what's the justification?
What about a PP for previous East? Did their infraction cause the board to be unplayable? Not initially, but it did once all four players had seen AS.
There is I think a general point about how much we should expect the players to know the law, particularly the less common aspects.