I’ll go you one better with the likely historical precedent for Niklas Luhmann’s zettelkasten numbering system: conscription numbers on Viennese houses in 1770s! https://hypothes.is/users/chrisaldrich?q=austria+tag%3A%22Niklas+Luhmann%22 Alberto Cevolini & Markus Krajewski have relevant research. There are still a few missing puzzle pieces however.