pran, on 2018-July-25, 11:05, said:
Oh, I thought that was obvious?
It is not "your own misunderstanding" if you draw the wrong conclusion(s) from opponents misinformation. And such misinformation exists whenever an explanation is incorrect or incomplete in any way.
The way I understand Law 21A is that it applies when a player claims misunderstanding of opponents' correct information (and also if he claims that he has misunderstood his own side's agreements).
I think it also applies if the opponent alerts, but you decide not to ask for an explanation, but instead assume that you know what they're alerting about.
E.g. 1NT (2
♣ Alert!)
If you assume it's Cappaletti showing a single suit, but they're playing DONT, you have no redress.
The issue in this thread is when they explain, but the explanation doesn't include all details. Does 21A apply because you could have asked for more info rather than assuming, or is it MI because they should have mentioned those details in the first place. How much cross-examination are players expected to do to protect themselves from making unwarranted assumptions?
For instance, in my experience, most people who play Michaels and Unusual NT expect them to show at least 5-5, but 2-suited NT overcalls are more often at least 5-4 either way. So if I hear an explanation of these conventions that doesn't get specific about the expected lengths, I'm not going to grill them. I expect that players who have unusually specific agreements to disclose them proactively. Unless they play almost exclusively in an insular environment where everyone plays like they do, I think they know that they're not mainstream and a generic explanation will be misleading.