Fashion in the former GDR wasn't changing as fast as it did in the Western world.
So they probably had a decade or so to make such a pattern...
In the same were coats developed, they fitted out of the spot with almost no alteration. The system had to be learned in the apprenticeship or at least to understood.
Behind this system is the Rundschausystem hidden. In the GDR they had the Fachbeirat out of the most knowledgeable master tailors who where funded by the government
and also had their own tailor shops. In 1963 they already improved the Rundschausystem like it is today and still the Rundschausystem has not reached the GDR level.
This so called Einheitssystem was prepared for computer use already. Every point of the cutting system around the body was covered by an accuracy of under 5mm.
The Fachbeirat produced proportions which are still unknown today by the Rundschausystem. In the GDR the tailoring were taught on a high level in the theory.
The system was only taught in the cutting school of Modeinstitut of Berlin and in apprenticeship, there is no book published only loose copies existing.
The system is not handy on the first site but it is not that difficult when you have a complete overview of the Rundschausystem you can handle this GDR system.
East German tailors, there are only a few left, they still use the system as soon as they gone the system is out of reach.