[barmar]

Vampyr, on 2017-August-22, 14:52, said:

That depends. I would never make such a rebid with a hand in my opening 1NT range. I play a weak NT, so I guess it is more dangerous as I would be overstating my hand and we could end up in a poor game, but anyway I have never considered it.

What do you bid instead? 2♥, even though you don't have the appropriate shape for a reverse?

This is what I meant by this being a problem for many systems -- something has to be distorted.

[barmar]

Zelandakh, on 2017-August-22, 08:19, said:

Well I would rebid 2♦ and some others would rebid 2NT. Either way it is so obvious that I would expect any longstanding, advanced pair to have an agreement and LOLs in the club not to have any idea.

With may last partner I had the specific agreement that 1♦ - 2♣; 2♦ was F1R and could specifically be just 4 diamonds. One of the first times it came up, my partner forgot to alert so I duly announced it to the table at the end of the auction after I became declarer. The opps in turn were extremely upset when I turned up with the usual hand type (weak, 5+ diamonds) and thought I was trying to mislead them. Sometimes full disclosure is "damned if you do, damned if you don't" .

They're just wrong. If partner fails to alert/explain "could be X", and you correct this, they should not assume that you're describing your actual hand, you're just explaining your agreement. "Could be X" doesn't mean "Is X".