Oh, being all bound by the objective historical conditions ... what’s wrong with you? It’s not like this stuff really happened anyway!
Actually, in a way, it’s not like this stuff really happened anyway. A history is one thing, and a historical fiction is a step removed, and a fantasy jumping off from a historical setting is something else again.
But on the other, other hand ... go with what’s in the text.
Most movies anymore seems to be either remakes or based on books.
The norm seems that both types should be done as poorly as possible.