All the novels mentioned here fall under the genre of historical
fiction which must be based on historical fact. If one takes the
trouble to write a book, why not base it on the actual history?
It is the duty of a good writer to check and recheck the facts.
There is a certain amount of research done for any novel,
even one that is not historical. There is nothing worse than
reading something in a book that one knows is not true or
plausible. Such books are usually ripped apart by the critics
and its readers tend to feel ripped off as well.
That is not to say that a writer of historical fiction cannot add a
fictional place, etc., but everything contained in such a book has
to be historically accurate. Usually these writers will separate
truth from fiction in a foreword or author's notes.