Some books have existed for many centuries almost unchanged, wizards that have tried to change such books are quickly reviled and thus no change happens, after all, such books, the history within, are like preserved artifacts. But, who is to say they have all the information from when it was created? It is a good thing to always assume that there is missing information from them. One only can hope that said information won't be needed in the future.
Extract from Hogwarts: A History, 3rd edition -Edited by Dillard Fiddlewood Editor's note: Removed the part about the castle supposedly having sentience or that it can take charge if its inhabitants are threatened. Bah! Such nonsense must have been thought by some mud-ggleborn, evidenced by the author's name. There's no proof of anything like this!
(...) It's been said in times past that, even if the castle is not as old as other castles, such as the legendary Slytherin's Keep, or Godric's Castle, Hogwarts has attained a higher level of ambient magic than those previously mentioned. Some people think that perhaps Camelot or Avalon had a castle like this, but that is something a Lovegood could probably research. Coming back on topic, Hogwarts got such level of magic thanks to the people who live on it, the teachers, house-elves and the students constantly casting magic, leaving traces of magic on every single rock of the castle. It is a theory that his caused some strange phenomena, such as the moving staircases, since there is no evidence nor registry of any of the Founders enchanting them like that. . It's been two hundred years since the last Founder passed away, and since then it has always been said that the castle, the school, is one of the safest, if not the most, place in all of the country. But how does this relates to what was previously mentioned? It is the opinion of this writer that, should the inhabitants of the castle be in danger, by either forces attacking the castle itself, or from someone within, if the Lord of the Castle -now called Headmaster- does not take action, the castle itself will, and if it does, it will find the previously mentioned Headmaster in abeyance of his duties, and will enact its own safety measures. I can only hope that if this ever happens, that it is soon, for the more time it passes by, the castle will receive more magic, and perhaps its response will be far more harsher. --Addition by Alvin Beddington