I asked a similar question recently & got this answer from pjgh
"All "1912s" are post-1919. Prior to that, as GEM they were Damaskeenes and there were no pre-1919 Ever Ready. In 1919, GEM was bought out by the American Safety Razor Co. Inc. (who held the Ever Ready trademark) and became the American Safety Razor Corp. (this helps date 1914s). 1930, GEM ceased the 1912, but re-branded it the "GEM Junior" on the back (and ceased altogether in 1933 ... picked up as the Star brand). 1930 on we have Ever Ready 1912s. The shape of the comb can help date GEMs - the very corners bow out on the earlier ones and all Ever Ready, post-1930 the corners are sort of trimmed. Ever Ready (post-1930 and US) had the same shape but the old shape remained for British made. Late British (from the end of the '40s) started to come with aluminium handles"
I hope this helps