I can’t speak for the GB but I have known a good many people who wholeheartedly believe what they know as “The Truth” . It doesn’t matter what evidence is pointed out to them because they”lLet God be found true though every man be a liar” . They’ed Say “ Jehovah will clear that up in his time” and carry on. The belief that “The Truth “ is true is stronger than the most basic science fact . They would believe the moon was made of cheese rather than doubt their faith.
As for those at the top , I recall Ray Franz writing that they had little time to do basic personal study . So take a belief like the 1914 date they believe it because it is accepted and would never go back to open mindedly reconsider it . They have spent so many years in the institution that they cannot think outside the box and I can imagine that in the higher parts of Warwick, the power of “ group-think” is immense.