Prior to 1950, Chinese control of Tibet, certainly central Tibet, was never so tight as it has been in the post-1950 era, and these relations were always within what we think of as imperial (often Mongol or Manchu and not simply "Chinese") and not nation-state frameworks. Chinese control of Tibet is now complete. So your notion that autonomy is subject only to trivial degrees of difference doesn't seem satisfactory to me. It misses the complexity of the thing. You want a yes or no answer for all time, including the time of archaic Chinese and Tibetan civilizations, that will fit your current understanding of how nation-state boundaries ought to be drawn.