In that experience part of the problem was that those who disagreed with the group were purged out of the group one way or another, either because they chose to exit out of disgust or because they were driven away, or something in between. So there was a "survivorship bias" in the group, where "surviving" sort of meant staying with the group.
It's interesting to think about how this applies to your WWI examples, where the people in the position of admitting mistake are still alive, and there's a very literal survivorship bias with regard to group membership.
Anyway, when you have an entity that can change in composition, it affects what is involved in admitting to mistakes, because the people making the mistakes might be different from those who would admit to them.