See more in this blog. The blogger used these maps to show that Tibet was part of the Qing Empire (to counter claims that it was independent all the time before 1951).
IMHO all these history talks are trite. To us geographers (with better knowledge in history) we are more interested in these old maps themselves.
Meanwhile, here is a full collection on Harvard Yenching Publication on old China maps. There is a 1939 map published in Japan, where Manchukuo, Mongolia and Tuva were independent, while Tibet was labeled part of China. (Apparently Japan did not recognize USSR's annexation of Tuva)