Just got a 99F. S/N 9540xx which by the numbers in Royal’s book would place it in the middle part of 1958. But the lever boss code is 16 I which would be 1957. Is this unusual? On the receiver side under the stock is 15 I the best I can tell. That would indicate a different inspector? Rear sight is missing. Numrich has lots, but picture is different than the one in Royal’s book- any ideas on where to get one that is pretty sure to be corrret?