A person' s personality is linked to that person' s genes. And since a person' s genes do not ordinarily change over time, it follows that a person' s personality remains unchanged with the passing of time.
The statement "The way historians understand the First World War is related to what happened in that war. But what actually happened in that war cannot change. Therefore, historians' understanding of the war cannot change" is most closely parallel in its reasoning to the flawed reasoning in the argument above.