I've found some mention of hidden dates on Canadian stamps in previous posts but not much.
When I first learned of this many moons ago I had fun in finding them on all the stamps I had and as every new stamp came out the first thing I did was to search for the date.
Anyway I figure it should be fun to show them all especially the engraved ones.
Not every stamp from 1935 on has them but there are some stamps which should have them but I can't find them, so perhaps some forum member can help me locate it.
Scott Monthly had a good article about hidden dates & designer's initials in their January 2010 issue.
Lets start off with the Air Mail Special Delivery ones.Scott CE1 1942 Scott CE2 1943
Not only was the value re-engraved but also the date.