First what are your references?Looks like I am going to have to be the one to rain on the parade.
According to my references, Sestroyetsk didn't begin making the M1891 rifles until 1892. Production ran from 1892 to 1918. That would place the tang somewhere between 1910 and 1918.
Second according to most references, Tula and Izhevsk didn't make rifles until 1892 either and some even say they used tooling from Chatellerault! I have personally had 91 dated Tula and Izhesk rifles in my hands. Your references are most likely wrong.