The problem remains: if the culture of a province determines the aspect of its nobility and said nobility was historically not at all what the game would represent, then we should either treat culture as "a recipient of nobility culture" (in which case, I'm afraif half of Northern Italy should be painted Occitan, from Nice to Monferrato) or make specially complicated mechanics.
Sometimes it doesn't work either. Like English lords spawning all the time in its French domains, insensible to the fact that in Anjou, Poitou and Aquitaine, Englishmen had little and less to do at the side of the French and Aquitan dynasties and barons. Yet the game has it that way.
This is the everlasting problem of the courtiers and noblement in Jerusalem. Frankish Jerudalem should spawn Frankish, Occitan, Norman and other European noblemen. Instead, you get "Gerrard de Al-Harran" and there's nothign to do about that...
Culturally speaking, the game's an aberration, even, for not allowing even a degree of mixture in a time in which culture was so definitely not like today, and so totally not like the game has it.