Does anyone have any information on the ethnic composition of Tibet prior to 1950, especially in the eastern regions of Kham and Amdo?

The areas are so sparsely populated that I find it hard to believe that they have always been "Tibetan". Even in Kham today, 33% of the people speak Qiangic languages and practice various Bon religions. What other peoples have historically settled in the Tibetan Plateau?

What other peoples (Uyghur, Han, Mongol, Lisu, Naxi, Mosuo, Baima etc) have lived in Tibet? When, if ever, did they leave? And what was their relation to the Tibetans of Lhasa?

there's the Lhoba and Moinba? from what I read.. they were previously classified as "Zang" or Tibetan, but they themselves requested to be acknowledged as a separate ethnic group. they are still Qiangic language speakers.