As part of my Architectural graphics coursework, I read about the perforated cards used in the 19th century containing digital information (via perforations) to control textile looms. Of course in relation to that course, the bridge was being built to the use of digital information in computer systems, but I claim it also applies to the original tissue patterns dating as late as the mid-1950's.
If we think about it, these perforated markings on the pattern allow us to control where we make an indentation in the fabric surface via tailor tacks, chalk or carbon tracing. The perforations also enable us to do aligning functions with the patterns when placing the pattern with respect to the grain of fabric or when placing a pocket or other application accurately on the fabric design.
Paper sewing patterns are a special part of developable surface exploration. I know so many of you have told me you are as excited as I am about the 2-D paper becoming a 3-D garment via darts, folds, tucks, seams, etc.
The perforated markings which create the dart at the keyhole neckline in the pattern of a blouse I started last night.