Or just actual history, right? Im reading a fantastic book on medieval history and it makes a point of noting how often histories by various of-the-time sources make the effort to create mythical tie-ins for rulers and peoples (check out the Lebor Gabala Erann / "Book of Invasions" which more or less invents an entire history of the Gaelic Irish whole cloth, or many royal-tied writers drawing on religious and secular imagery together to create a chain running from Jerusalem and Rome twined to anoint their sponsor).
I was reading some fantastic posts the other day on Reddit about how perfectly messy The Elder Scrolls' in-game lore books are, because each one is written from the perspective of different peoples or even different sects or figures within a single people (and coupled with the fact that a bunch of the foundational stuff was Bethesda-fan-sourced or done by both employees and contractors!). It hits far more like the absurd mess of a real world than most fantasy stuff I've seen as a result.
If I wanted to point at a setting that sets more canon but is somewhere as messy, I might look at Dolmenwood. It has a pretty compact set of foundational lore to present players, but points out in the campaign book how each faction either knows different Truths or opinions about the world, and in some cases is actively suppressing things (eg: about certain bits of arcane lore, or the history of old gods of the wood, or the fact that the human and Breggle relationship is fairly Norman conquering the Saxons in vibe).
