I used to make fairly elaborate Christmas cards, and for a few years I made "advent calendar"-type cards, incorporating the traditional twenty-four "doors" which are opened, one per day from December 1 to December 24, to reveal hidden surprises. For this one from 1983 (I probably drew it the same month the Turtles were created), I created this top layer depicting a fanciful Christmas-themed landscape.
Then I drew this piece with the various images which would be revealed as each "door" was opened. This sheet would be glued (carefully, along the edges) underneath the top sheet.
But that couldn't be done until after I had carefully pre-cut along three sides, with an X-Acto knife, each of the twenty-four "doors" so that they could be easily opened by the cards' recipients. I think this was the step that finally put me off doing these things -- it was a lot of work! -- PL
P.S. The finished card measured 8.5 by 11 inches. -- PL