Scoring: MP
At my table the auction was
1♦ - 1♠
1NT - 2♣
2♠ - 4NT
5♥ - 5NT
6♦ - 7♦
P
At another table the auction was the same until South bid 6NT instead of 7♦, and GIB carried on to 7♠.
What I want to know is: why did GIB bid 7♠ over 6NT but not over 7♦? Does anyone have enough experience to predict when GIB will do this kind of thing?

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