Example 1 - Mistaken Explanation
The actual partnership agreement is that 2is a natural sign-off; the mistake was in North's explanation. This explanation is an infraction of law, since East-West are entitled to an accurate description of the North-South agreement (when this infraction results in damage to East-West, the Director shall award an adjusted score). If North subsequently becomes aware of his mistake, he must immediately notify the Director. South must do nothing to correct the mistaken explanation while the auction continues; after the final pass, South, if he is to be declarer or dummy, should call the Director and must volunteer a correction of the explanation. If South becomes a defender, he calls the Director and corrects the explanation when play ends.
Example 2 - Mistaken Bid
The partnership agreement is as explained - 2is strong and artificial; the mistake was in South's bid. Here there is no infraction of law, since East-West did receive an accurate description of the North-South agreement; they have no claim to an accurate description of the North-South hands. (Regardless of damage, the Director shall allow the result to stand; but the Director is to presume Mistaken Explanation, rather than Mistaken Bid, in the absence of evidence to the contrary.) South must not correct North's explanation (or notify the Director) immediately, and he has no responsibility to do so subsequently.
In both examples, South, having heard North's explanation, knows that
his own 2 bid has been misinterpreted.
This knowledge is "unauthorised information" (see Law 16A),
so South must be careful not to base subsequent actions on this information
(if he does, the Director shall award an adjusted score). For instance,
if North rebids 2NT, South has the unauthorised information that this bid
merely denies a four-card holding in either major suit; but South's responsibility
is to act as though North had made a strong game try opposite a weak response,
showing maximum values.