I used to spend hours checking the
Phase of
production on the Philatelic Archives site and found
all these amazing illustrations in what was
involved in stamp production at that time.
Photo of an essay by Emanuel Hahn the designer

Progress proof notation by LJ Mills Director of Financial Services
The letters in Canada should appear in the sky as though on a separate box

When I look at this imperf plate proof block I wonder what
this would go for at auction.

die proof, colour trial
32m green scratch no 103 Dec 16 9 blue. 
What was meant by
32m green scratch no 103 ?
Also accessible are biographies of designers and engravers.