Accuracy is paramount in every detail of a work of history. Here's my rule: Ask yourself 'Did this thing happen?' If the answer is yes then it's historical. Then ask 'Did this thing happen precisely this way?' If the answer is yes then it's history if the answer is no not precisely this way then it's historical drama.
If I could have anyone on speed dial it would be George Clooney. He seems like a cool guy who would give good advice.