[thorvald]

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Now this hand is difficult to bid after a 15-17 NT, so Pass is probably best, unless you feel for a penalty double.

Now after the transfer Double is T/O, but what is 2N ?

I don't think we can find any bridge player, that will agree with the GIB-definition:

Invitational to 3NT game -- 20+ HCP, 20- total points and a ♠-stopper

[smerriman]

2NT is basically undefined here, so gives a weird description like many other undefined bids. GIB wasn't "programmed to show 20 points"; that got autogenerated from an unrelated sitation, and GIB will never make the bid.

[thorvald]

It seems adding a rule with the following constraints:

Bidding NT with a passed hand opposite a passed partner is minors - any level - according to losers, and less restrictive in pass-out situation

would be a fine improvement