1) How did you find the Evenk (sic) in the countryside? Did you just wander around and ask (in Chinese) everybody you saw if they were Evenki? How upset were the Chinese guards?
2) I remember reading somewhere that the Ket were driven northward not by the Evenks, but that they moved themselves northward to avoid being stuck inbetween the Russians and Tatars. Both groups demanded tributes/taxes from the Kets, but the Kets could afford to pay only one. Thus, they moved north so they would be completely in Russian territory. They also didn't have to worry about Tatar attacks there.