Historiography might come into it. The events will stay the same but interpretations of the event in question over time will change as people look back on the past and point out X or Y. It may be another generation looking back without the prejudices of the previous generation i.e. history of Africa would be different in books from the 1930s compared to 1950 compared to 1990.

A more grippable example would be the Jewish holocaust where history books written early on about the subject mentioned how the German people were oblivious to the events, various historians have written on the subject with different arguments on whether or not the German people knew about it or more importantly were complicit in the killings of the Jewish and other ethnic races. An example would be Daniel J. Goldhagen with his book "Hitler's Willing Executioners" who argues that the German people were willingly helping the SS in the killing of the Jews.

So my advice would be to read the book however also read others to get a more objective view and do not take the conclusions offered as truth as it may be steeped in the prejudices of the day.

Quite a few. In the field of ancient history, for instance, new texts are regularly found and this regularly necessitates re-evaluation of our accounts of ancient history(one can only be startled for instance by Gombrich's claim that Hammurapi was "one of the first to rule over the whole region" when the first model for universal kingship that was emulated all the way down to the end of Mesopotamian civilization was established by Sargon of Akkad over 500 yeas before Hammurapi, nor would they be depicted "sacrificing to Baal" since Baal is not a sungod and he was mainly worshipped in the Levant, and besides the Phoenicians were hardly the first people to send letters!). When Gombrich wrote this book, the study of Hittite was in its infancy and the project of publishing the tablets from Hattusa was only just beginning, Sumerian was much less well-understood than it is today, Ugaritic had only just been discovered, and we had not yet discovered several extremely important cuneiform archives such as those at Ebla and Sultantepe. Furthemore, continuing archaeological research improves and aguments the historical picture provided by new textual discoveries; for example continuing excavations at sites in Anatolia like Gordion and Sardis have dramatically improved our understanding of how Persians and Greeks interacted and how the Achaemenid empire governed its provinces.

Keep in mind that new evidence is constantly discovered, as well. For instance, histories of WWII written before ULTRA documents were declassified aren't wrong per-say, however, they are not as complete as one with the new information available.