The table you reference contains a well-known error. The third column is actually just a cumulative total of conversions, not serial numbers. If you think about it, converting all those arms in serial number order would have been a logistical nightmare to no practical purpose.
Quote:Model 1911 Carbines (Karabiner)
Converted from Model 1889/1900 Short Rifles and Model 1905 Cavalry Carbines
Year Quantity Serial numbers [wrong!]
1913 1000 1-1000
1914 8000 1001-9000
1915 8000 9001-17000
1916 8200 17001-25200
1917 900 25201-26100
1918 100 26101-26200
1919 70 26201-26270
1920 65 26271-26335
The partial serial given is that of a 1900 short rifle originally manufactured in 1908. The "P64" is most likely to mean "Privatized in 1964". Pictures could assist positive ID.
Nothing unusual.