3NT for GIB is 25-27 balanced. Over that, 4♦/4♥ are Texas, 4♠ undefined, 4♣ Gerber and 4NT quant (5-6 HCP). There's no way to find a major-suit fit, no way to make it pick 6 or 7 and there are no followups after Gerber.
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3NT opening - poor followups
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