mycroft, on 2021-April-02, 10:28, said:
I know players for whom 4NT is ace-asking, no matter what the auction. Even this one. For them, answering aces would be an LA.
...
I totally understand the "he heard there was a system screwup, so he passed ASAP and hoped" - I've ruled against that any number of times. But here, I don't see it, if the pair has "quantitative 4NT" in their vocabulary. Which, if they're playing crazy inverted splinters, I'm guessing they do.
This player certainly would consider 4NT to be quantitative if the explanation had not reminded him of the actual agreements.
And I'm pretty sure his rapid pass was an attempt to make things easier for everyone, certainly not in the hope of a better result.
I don't think he knew if it was appropriate or even legal to respond with keycards.
He is an ethical young guy and I imagine would have been happy to explain his forget to the opponents before lead was chosen, had he known that was legal (not to stir up a previous thread, but the issue is there).
mycroft, on 2021-April-02, 10:28, said:
I am not so sure that there is no MI - I would check if this was a "no mutual understanding" case.
The system card is there, and he would recite it word for word if asked.
If you were his club TD you would know that he occasionally forgets some partner-specific stuff all the same, which you might consider modifies this agreement.
His partner doesn't seem to take any account of that possibility in his bidding.
So I would say borderline at most, and not relevant to the 4NT bid issue.