[lycier]

iandayre, on 2016-March-11, 14:38, said:

And here is another hand with the same theme. Opener's 3C can show up to 22, but the 1NT responder can (and does here) pass it. Gotcha again.

http://tinyurl.com/heps63g

Just now I studied Iandayre's hand repeatedly, it so happened that I found same bid with different explanations at the different tables.
Robot : basic Gib
Table : Teaching table and bidding practice table (china bridge club)
BBO version : web-BBO client

1- Here is Iandayre's hand.

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2- When I open Teaching table :

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4♣ says " 6+♠,19-hcp,twice rebiddable ♣,biddable ♠,20-22TPs ".
It is a good explanation, just like a picture bid, I agree.

3- However when I open Bidding Practice Table :

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4♣ says " 4+♣,21-hcp,rebiddable ♠,19-22TPs ".
It is not same with teaching table, worse explanation. I don't know the reasons,just reporting.

[lycier]

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[Bbradley62]

lycier, on 2016-March-11, 19:29, said:

2- When I open Teaching table :
4♣ says " 6+♠,19-hcp,twice rebiddable ♣,biddable ♠,20-22TPs ".
It is a good explanation, just like a picture bid, I agree.

3- However when I open Bidding Practice Table :
4♣ says " 4+♣,21-hcp,rebiddable ♠,19-22TPs ".
It is not same with teaching table, worse explanation. I don't know the reasons,just reporting.

I disagree with your analysis. The second description is a much better explanation. The first says twice rebiddable ♣; biddable means 4 good ones, rebiddable means 5 good ones an twice rebiddable means 6 good ones. North does not have 6 good clubs. Should he need 6 good clubs for this bid?

[lycier]

IMO, I would like to define 4♣ as a (forcing) picture bid to resolve fifferences with 6-4 or 6-5 distributions of double suits.