barmar, on 2017-October-26, 10:48, said:
You don't need to know the offender's thought process, you can infer it from the replacement.
If he replaces 2NT with 3NT, the IB was presumably intended to be natural, so you allow it with no further rectification.
If he replaces it with 4NT, it was presumably intended to be unusual, so you also allow it with no further rectification.
This is a long-winded way of saying that both "natural" and "the minors" are meanings that could be attributed to the withdrawn call, so both 3NT and 4NT are available as penalty-free replacements. There's no need to think about what was intended.
barmar, on 2017-October-26, 10:48, said:
It's possible that a player who intended 2NT as unusual could replace it with 3NT. But making a replacement with a totally different meaning than originally intended is not likely to be successful, so the opponents will rarely be damaged (I know, I just threw down the gauntlet to Lamford). And if it is, the TD will likely be able to adjust based on 27D.
I agree with the first part, but if the offender bid 2NT to show the minors, was made to retract it because it was insufficient and chose to replace it with a lucky 3NT, I don't think there's any way the TD could adjust the score unless their partner took some kind of unexplained action that could have been suggested by the withdrawn call, or the offender could been aware at the time that the irregularity could well damage the opponents (law 72C). The offender didn't get to 3NT with the help of the insufficient bid (law 27D); they could have bid it immediately if they'd wanted to.