Multiple teams-of-eight, IMPs -> VPs
1♣ was prepared (might be only a 3-card suit)
1NT was alerted and explained as the unbid suits
Result: 2♠(E)=, NS-110, lead ♣3
I was called when dummy was displayed. I asked EW what their agreement was about 1NT. West said he thought it was natural, but neither he nor East could provide convincing evidence that their interpretation was the correct one. I asked West why he had not called the director to correct the misexplanation before the opening lead was faced. He apologised for the omission.
At the end of play I was recalled by EW, who wanted to know whether West could legitimately pass 2♠, and also thought that South might have led a trump had the explanation been corrected in time. EW play full transfers over 1NT openings (2♠ -> ♣); their convention card states that their responses to 1NT overcalls are as over 1NT openings.
How do you rule?