A quick way to tell if it was made before or after 1909 is to see if the gun has the positive hammer block and the new style trigger guard machining with the top "V" of the trigger guard flat with the frame. If there is a "step" from the frame to the "V" of the guard, it is an old (pre-1909) model.
The .455 Eley, .476 Eley and the .450 Eley, were among the first calibers for the New Service and the .455 remained in production at least through WWI, being sold not only to the RNWMP (RCMP) but also to the British government after 1914. (After WWI, the Canadians ordered New Service revolvers, but in .45 Colt, not .455.)
Jim