Oh yeah? I had Ming rebels pop up in Roh in my Minghals game and they created Ming in Roh. With primary culture Khorsani.Its got nothing to do with provinces being historically owned. Its merely related to how many TAGs of that specific primary culture (same culture as in province in question) are available in the data base (they exist on the list but do not exist on the map). Some TAGs are purposely disabled so that they would never get spawned - for example unification TAGs will only spawn if they exist on the map as cores (so effectively only if someone enacted unification decision). Otherwise youd see Germany, Russia, Italy etc occasionally pop up.