According to the 1907 Fourth Division engine service seniority board F.C. (Franklin) Beatty was No. 7 in seniority. The list, on file at the R.W. Richardson Library at the Colorado Railroad Museum, does not give his seniority dates but we can assume it was after 1881. The was the year John Law, the No. 4 engineer, was promoted to hoghead. Beatty was off the railroad by 1920.
L.L. Dunbar was no. 48 in 1907. He also didn't have any seniority dates but he was one ahead of Charles L. Arnell, who was hired as a fireman on 10-04-1900. Dunbar also was out of the engine service by 1920.
I did not find Tom Roberts' name on the 1907 list.