Given that the kingdom of Asturias ceased to exist in 924, the game would spend more time with the kingdom not existing than with it existing. And if the kingdom of Asturias was treated as the only Christian kingdom-tier title in Iberia, it'd be impossible to represent the partition of the kingdom into León, Castile and Galicia (and later Portugal). I mean, how could the game mechanics represent a kingdom disintegrating into three duchies? Nevermind how the transition of kingdom of Asturias into the kingdom of Léon would be handled, or the unification of the kingdoms of Léon and Castile.
As for four other counterpoints:
- Danzig isn't part of de jure Lithuania, it is part of Pomerania instead (under the duchy of Pomerelia).
- Zaporozhia really shouldn't be the de jure term for the region of the Pontic-Caspian Steppe south of Rus'. Then again, what other term would fit the region that roughly compasses the area ruled by Pechenegs, Cumans and Crimean Tatars?
- Same goes for Caucasus, although in the case of Caucasus, I would argue that the entire region is in need of an overhaul, with more provinces, cultures and religions, which would allow the current kingdom of Caucasus to be split into smaller and more realistic kingdom-tier titles (like Circassia and Alania). I mean, currently the Caucasian duchies are the size of small European kingdoms, and the counties are the size of small duchies, so the region really would benefit from more detail.
From what the devs have told us about the succession laws, primogeniture becomes only available relatively late into the game, so it is reasonable to assume that in 1066, the Spanish nations are unable to pass primogeniture laws.