Yeah, it used to be that the Astronomican was located in the Himalayas, but the earliest mentions of the Imperial Throne implied it lay where GW headquarters is (Nottingham? I forget). I think later the Astronomican and Imperial Throne were sorta conflated, just going off memory. But at least the the HH novels explicitly described the palace complex and it's in the Himalayas.
While I'm not a huge fan of the HH novels, there are some neat tidbits about pre-Unification Terra, with various dystopian, post-apocalyptic empires that the Emperor eventually conquered. Not much, but the kind of stuff I like to spin off from.
As for the newest lore, I'm overall pretty okay with it. Expanding the Eye of Terror was a ballsy move, and one that I think has been pretty fruitful. The rest is... fine, I think? I'm not crazy about them trying to justify the Primaris marines lore-wise, but hey, I can't really force myself to get too worked up about it either.