6D made on the play shown.
The event was played with screens. On the W/S side of the table the 3C bid was described as natural (not alerted and not asked about, 4C was asked about and described as natural). On the N/E side of the screen the 3C bid was asked about and described as Checkback (written response confirming this).
On the play a spade was led. W won the ace and, thinking declarer/N held something like Kxx - AKQJx Axxxx, returned a diamond. As such the slam made rather than going off - as it would have if W had given E a spade ruff.
At the end of the play the difference in explanations came to light. S stated that 'Natural' was the correct explanation for 3C and that describing 3C as Checkback to E was the error - so W had had been given correct information throughout and the result should stand.
The NS pair had a well filled in, detailed, convention card which does not mention Checkback being played over 2NT (but does mention, for example, 2-way Checkback over 1NT). The card is linked below:
NS Detailed Convention Card
The Tournament Director ruled that the result should stand (6D making) - as West had been given correct information throughout the hand.
Do you agree?