I now have definitive written proof of a numeric indexing system (delineated in a popular textbook for secretaries, and published by a company which did significant business in Germany) from the mid-1920s with increasingly more detail into the 1940s and a fifth edition published in 1950. It’s exactly like, but notably predates, Niklas Luhmann’s alphanumeric system which he started in 1952. I’ll write up some of the details shortly with specific references, but thought I’d tease it here a bit first.
@chrisaldrich tease some more, please!
Is it Technik des wissenschaftlichen Arbeitens by Johannes Heyde?
No, most of us have known about Heyde since at least August of 2022. There are some tangential suggestions to be found there certainly, but not the decades-long alpha-numeric practice I’m talking about presently.