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.
I think Whitman more than any other poet possessed the gift of revealing to others the beauty of everything around us the beauty of nature the beauty of human beings.