Here's Biger on the Wakhan corridor:

"Afghanistan acquired a common boundary with China by the terms of
the 1895 Anglo-Russian agreement by which the Wakhan strip and Little
Pamir mountain range became Afghan territory, thus separating the
possessions of Russia in Central Asia from British India. The Chinese
government did not participate in the boundary negotiations; in fact,
it only became aware of the line 68 years later, in 1963. A Sino-
Afghan boundary was drawn, while China and Pakistan also reached a
boundary agreement at that time, forming a junction with the Sino-
Afghan boundary ..."

Grant