I located this very handy guide on the Stamporama website. Very useful as the early Newfoundland issues have several very dangerous fakes out there. Spiro, Oneglia, Fournier. The characteristics of genuine examples are juxtaposed to the forgeries.
http://stamporama.com/articles/disp...AucTLhay2OEgEnjoy, and check the site out there are quite a few good articles noted.