A rule discovered halfway through deserves a fairer response than retroactive blame.

Rules that surface late are a failure of communication before they are a failure of compliance. Somebody knew, somebody assumed everyone knew, and the person now being corrected was working from what they were actually told. Treating that as carelessness converts a system problem into a personal one, and it teaches everybody to hide the moment they find out. The reasonable response is to fix the point where the rule was supposed to be visible.

If you have to raise a late rule with someone, say plainly that they could not have known it. Then ask where it should have appeared, and put it there.