A bit strange --- The date on the tang is clearly a 9 and a 1, it is even more obvious when looking at the tang with a small light, AND there ISN'T a hole like in the picture from PZ93C.
According to Lapin's book the 9 and 1 indicate the date of 1891. Lapin's book also has a few errors (like any other military firearms book so I am certainly not saying this as a criticism) , such as stating that the earliest production of the M91 was in 1892. Ted's site has a picture of a Mosin dated 1891 on the top of the barrel, so there were definately M91's produced in that year. I just think finding a receiver dated in the first year of production is pretty dang cool.