I am thinking late 1907 or early 1908 based on serial number research to date:
Estimated Pierce Serial Number Range per Year
1895 8,000 (0-8,000)
1896 15,000 (8,001-23,000)
1897 15,000 (23,001-38,000)
1898 15,000 (38,001-53,000)
1899 15,000 (53,100-68,000)
1900 15,000 (68,001-83,000)
1901 7,000 (83,001-90,000)
1902 10,000 (90,001-100,000)
1903 10,000 (100,001-110,000)
1904 8,000 (110,001-118,000)
1905 5,000 (118,001-123,000)
1906 5,000 (123,001-128,000)
1907 7,000 (128,100-135,000)
1908 8,000 (135,001-143,000)
1909 7,000 (143,001-150,000)