I just bought a book at a gunshow, The Bellgian Brownings. It has taken about a year of gunshows before the book surfaced again. The book states that Mod 1900 serial number 100,000 was celibrated on Aug. 4, 1904. Therefore, we know mine was produced later than 1904.
The book also has approximate production of the Mod 1900 for various years or groups of years and from that one can estimate seial numbers for the years.
From this I suspect that mine was manufactured in late 1905 or early 1906.
The following are approximate and should help others trying to track down the age of their FN 1900's.
1900-1901 10,000 FN 1900 pistols serial # 1 to 10,000
1901-1902 21,700 pistols produced 10,001 to 31,700
1902- 1903 40,000 produced serial # 31,701 to 71,700
Aug 4, 1904 serial number 100,000
1903-1907 328,300 produced serial # 71,701 to 400,000
1907-1910 275,000 produced serial # 400,001 to 675,000
1910-1914 49,550 produced serial # 675,000 to 724,550
It also has a discusion on the slide legends stamped on the firearm and how they differed during the production run. Mine is not the earliest, but the second earliest style of side legends.
I would recommend the book highly to anyone insterested in the FN Model 1900, Model 1910, Model 1922, or HP.