Revoke by dummy
While directing a club session yesterday I came across a situation that was new to me.
One player had mis-sorted her hand, putting the S6 in a long club suit, and appearing to be short in spades. This hand became dummy, and none of the four players at the table noticed until after a spade had been (invalidly) ruffed in dummy, and at least one more trick had been taken by declarer. At about trick 8 they noticed, and called me. I could not find this situation described in the Law Book. I consulted two other (very experienced) directors, to whom it was also novel. We concluded that as all parties were at fault for not noticing the error, the most approriate response would be to award average-minus to both pairs.
What is the definitive ruling here. please?