Of course they are. The challenging part is reading different accounts of the same events, and attempting to discern the truth. For example, was Edison a good guy or a bad guy? Did he invent the lightbulb or steal it? And if you find something interesting, you can dig into it and find out more. Not so with a novel.

Fictional universes evolve into 'canon', where certain explanations are correct and others are dismissed. Star Trek, Star Wars, etc., famously have 'canon'. People get wrapped around the axle arguing canon. This is ridiculous, as it's all made up nonsense.