With what your seeing some sort of method has to be offered. It wasn't lazer scanned, CAD plans, water jet, or whatever,,,it was the 1930s/1940s... What would the method of manufacture be??
Bottomline.
Silver casting at that time in Germany was not method of production of jewelry. Look at other Otto Gahrs firm products - there are only die struck or hand made from scratch things.
There are less original rings than you think, much less...