My impression is that human brains are very much of a pattern, that under the same conditions they react in the same way, and that were it not for tradition, upbringing, accidents of circumstance, and particularly of accidental individual obsessions, we should find ourselves—since we all face the same universe—much more in agreement than is superficially  apparent. We speak different languages and dialects of thought and can even at times catch ourselves flatly contradicting one another in words while we are doing our utmost to express the same idea. How often do we see men misrepresenting one another in order to exaggerate a difference and secure the gratification of an argumentative victory!
—H. G. Wells, “The Idea of a World Encyclopedia.” Harper’s Magazine, April 1937. https://harpers.org/archive/1937/04/the-idea-of-a-world-encyclopedia/.

I’ll agree with Wells that most of our difference here is nitpicking for the sake of argument itself rather than actual meaning.

Because we’re in a holiday season, I’ll use our holiday traditions to analogize why I view things more broadly and prefer the phrase “zettelkasten traditions”. Much of Western society uses the catch-all phrase “Happy Holidays” to subsume a variety of specific holidays encompassing Christmas, Hannukah, New Years, Kwanzaa, and some even the comedically invented holiday of Festivus (“for the rest of us”). Each of these is distinct in its meaning and means of celebration, but each also represents a wide swath of ideas and means of celebration. Taking Christmas as an example: Some celebrate it in a religious framing as the birth of Christ (though, in fact, there is no solid historical attestation for the day of his birth). Some celebrate it as an admixture of Christianity and pagan mid-winter festivities which include trees, holly, mistletoe, lights, a character named Santa Claus, and even elves and reindeer which wholly have nothing to do with Jesus. Some give gifts and some don’t. Some put up displays of animals and mangers while others decorate with items from a 2003 New Line Cinema film starring Will Farrell. Some sing about a reindeer with a red nose created in 1939 as an inexpensive advertising vehicle in a coloring book. Almost everyone differs wildly in both the why and how they choose to celebrate this one particular holiday. The majority choose not to question it, though some absolutists feel that the Jesus-only perspective is what defines Christmas. 

I have only touched on the other holidays, each of which has its own distribution of ideas, beliefs, and means of celebration. And all of these we wrap up in an even broader phrase as “Happy Holidays” to inclusively capture them all. Collectively we all recognize what comprises them and defines them, generally focusing on what makes them mean something to us individually. Less frequently do we focus in on what broadly defines them in aggregate because the distribution of definitions is so spectacularly broad. Culturally trying to create one and only one definition is a losing proposition, so why bother beyond attributing the broader societal definitions, which assuredly will change and shift over time. (There was certainly a time during which Christmas was celebrated without any trees or carols, and a time after which there was.)

Zettelkasten traditions have a similar very broad set of definitions and practices, both before Herr Luhmann and after. Assuredly they will continue to evolve. One can insist their own personal definition is the “true one”, while others are sure to insist against it. Spending even a few moments reading almost anything about zettelkasten, one is sure to encounter half a dozen versions. I quite often see people (especially in the Obsidian space) say that they are keeping a zettelkasten, when on a grander scheme of distributions in the knowledge management space, what they’re practicing is far closer to a digital commonplace book than something Luhmann would recognize as something built on his own model, which itself was built on a card index version of a commonplace book, though in his case, one which prescribed a lot of menial duplication by hand. The idiosyncratic nature of the varieties of software and means of making a zettelkasten is perforce going to make a broad definition of what it is. Neither Marshall Mathers nor Chris Rock are prone to call their practices zettelkasten—primarily because they speak English—but they would both very likely recognize the method as a close variation to what they’ve been doing all along. 

Humankind has had various instantiations of sense making, knowledge keeping, and transmission over the millennia classified under variations of names from talking rocks, menhir, songlines, Tjukurpa, standing stones, massebah, henges, ars memoria, commonplaces, florilegia, commonplace books, card indexes, wikis, zettelkasten and surely thousands of other names. While they may shift about in their methods of storage, means of operation, and the amount of work both put into them as well as value taken out, they’re part of a broader tradition of human sense making, learning, memory, and creation that brings us to today. 

Perhaps it’s worth closing with a sententia from Terence‘s (161 BC), comedy Phormio (line 454)? 

Quot homines tot sententiae: suo’ quoique mos.

Translation: “There are as many opinions as there are people who hold them: each has his own correct way.” Given the limitations of the Latin and the related meanings of sententiae, one could almost be forgiven for translating it as “zettelkasten”… Perhaps we should consult the zettelkasten that is represented by the Thesaurus Linguae Latinae?