History can't be a precise science as it relies too heavily on recollections of the past. Just because these recollections are put down on paper doesn't make them 100 percent true. Also people make up things for various reasons.
There was a time when only the wealthy had books and most people were illiterate. In those days books, including those dealing with history, were written to cater to a slim minority. Back in the 12th Century Geoffrey of Monmouth produced Historia Regum Britanniae (The History of the kings of Britain). Today this so-called history book isn't considered much of a history book at all. Much of the content is fictitious with propaganda aimed at making the prospective reader look good. Nowadays there is enough proof to say that the Trojans did not found the British nation. Even so, there is real history even in this book if you can manage to swim without sinking through the rest of it.
Here I am suggesting that at times looking at the author and his motivation or motivations to write history wouldn't be a bad idea.
Nowadays we can be beguiled by film footage from the past and hence accept a documentary as being for real even if others might find it questionable. We've seen it so it must be true, right? Well, film footage can be manipulated through its positioning in the narrative that goes with it. Important details can be left out.
In the past, in a less literate age, there was and remains a drought of evidence and information about the lives led by ordinary people. For the past three hundred years, however, there has been a flood of information about anything and everything. Part of what an historian has to do is sift through all this information to find what suits best his research. Things are left out because they must be left out. Choices have to be made and they are not always the right choices.
I have noticed of late that, in a lot of modern history books dealing with the 20th Century, Germany after 1918 and before 1936 tends to be a blank spot. It is just not dealt with. To me how Hitler got into power and how a people gave up democracy for something much, much worse is a story worth telling. Unfortunately, you have school kids nowadays that think the German people just went mad one day, put Adolf Hitler in charge of everything and began to make war on their neighbors.