Orkhun Inscription shouldn't be the UB, imo. it's native to the Orkhon valley in the Ordu Baliq
Also Bilge Qaghan should not lead them.. he's Eastern Gokturk too haha
I think the Gokturk UB is fine as it is, but you are right about the orkhun name. How about changing the UB name to something like "stone memorial' or "stone inscription"?
From wikipedia:
Spoiler :
The Göktürks have left artifacts and installations all over their domain, from China to Iran. But only in Mongolia have any memorials to kings and other aristocrats been found.
In addition, why would you have the Vietnamese start at 200AD? at 200ad they are just a rebellion, not much of a nation. They gained autonomy around 500ad and independence around 900ad, start southern conquest around 1000ad, so you may want to move them to later date and change the UHVs a bit. This will also present some challenge to Nanzhao and Khmer. At the moment all 3 are quite dull to play.