The basic beaver CASC collar came out in 1903....and was worn well into the 1930's by militia members of the Corps. The permanent ( reg force) portion of the corps were granted the title of Royal ( a theme in recent days)....the reserve portion remained the CASC until 1936.
Variations due different manufacturers and the fact that it was worn for over 30 years means that there are a large number of versions available. I haven't yet been able to date the different versions. I hope to one day.
Bill is correct ...the one on the right is an officers pattern. There are left and right facing collars.
I've just started a website....still lots to do...many pages not finished yet.
www.rcasc.com
Dwayne
Dwayne