Awhile back there was some discussion as to when the little flange was added to this part. According to the Releases it was on 5-22-14: "Called for a flange on the sides of the handle to be continued clear around the handle. This change was made for strength, also to make a better looking handle (Galamb.)"
FWIW, some other interesting notes on this part:
"6-21-10: Changed material from brass plate and polish to coppered brass plate and polish (Howard.)"
Then, on "2-17-11: To be black enameled when assembled, instead of being coppered brass plated and polished. Diehl.)"
Presumably, the entire brake handle's material and finishing echoed that of the pawl handle, so we can assume that the brass plated handle assemblies officially ended in February of 1911, though no doubt it continued for a short time until all the brass plated handles were used up; either as they were, or perhaps painting over the plating until they were gone.