From 650 CE Khazar nobles may be upgraded to CL.
But here is the question : MAT or MUST as it's "all" and not "all or none"
So a mandatory upgrade or an optional one
Must. There is no "may" mentioned in the list. The wording is "Upgrade Khazar nobles (from 650 CE)"
Wine quality and subsequently consumption sharply upgraded around this time . Hence changing nobility' behaviour ?