Paula Marantz Cohen draws our attention to it:
[Historical fiction] smooths out the inconsistencies in the past and fills in the unknown. As readers, we know this is being done—the genre tells us so—but so powerful is the seductiveness of coherent storytelling that it makes us forget. For years I carried around an image of Sir Thomas More as an exemplary man—honorable and pious, as represented in Robert Bolt’s play (and the subsequent movie), A Man for All Seasons—only to have my notion turned on its head when I read Hilary Mantel’s Wolf Hall. Mantel’s version of the character now supersedes Bolt’s in my imagination. I could go to the history books and sort things out for myself, but it is unlikely that facts would make much difference. The vivid representation holds sway.
(Video: A scene from Aguirre: The Wrath Of God, whose historical accuracy is assessed here.)