Can an alert be MI if the opponents don't ask?
This is a situation that was discussed on Usenet recently, inconclusively. The situation arose under ACBL rules but I don't think EBU rules would be any different in this situation.
The bidding went P, P, 2!d!, X; 2!s, AP. 2!d was alerted, but the opponents didn't ask what it meant.
It turned out that the opponents assumed (without asking) that an alerted 2!d would be Flannery (apparently the only common meanings in that club are Flannery and a weak two in diamonds). The 2!d bidder thought the bid was a weak two, their partner that it was Flannery. The defending side ended up missing a game in hearts that was bid by every other pair.
There was a UI issue here that needs addressing (a nonforcing 2!s over a natural 2!d is alertable under ACBL rules, so it looks a lot like the opener took advantage of UI to pass the 2!s bid). However, I'm interested in what would happen if the 2!s bid were nonforcing and nonalertable (it isn't alertable in the EBU because it was made by a passed hand), and no UI existed; is the incorrect alert misinformation if it isn't asked about? There seem to be two main viewpoints on the subject, "a weak-two 2!d is announceable (not alertable) and thus alerting it is misinformation", versus "there are plenty of alertable meanings for 2!d that look very similar to the weak-two bid, so the opponents assume a specific meaning at their own risk".
For what it's worth, I'm more inclined to the second view here: for example, "I can't remember whether we play 2!d as a weak two or as Flannery" is an alertable agreement (possibly even the actual agreement in this case!), and yet the 2!d bidder's actual hand is a strong possibility in that case. It's enough of a corner case that I think it's worth discussing, though.
(This, is, of course, yet another reason to always ask when a bid is alerted!)