Merchants and traders have a waste book (Sudelbuch, Klitterbuch in German I believe) in which they enter daily everything they purchase and sell, messily, without order. From this, it is transferred to their journal, where everything appears more systematic, and finally to a ledger, in double entry after the Italian manner of bookkeeping, where one settles accounts with each man, once as debtor and then as creditor. This deserves to be imitated by scholars. First it should be entered in a book in which I record everything as I see it or as it is given to me in my thoughts; then it may be entered in another book in which the material is more separated and ordered, and the ledger might then contain, in an ordered expression, the connection sand explanations of the material that flow from it. 
—Georg Christoph Lichtenberg, Notebook E, #46, 1775–1776, as translated in Georg Christoph Lichtenberg: Philosophical Writings
In this single paragraph quote from his own notebook, Lichtenberg, using the model of Italian bookkeepers of the 18th century, broadly outlines almost all of the note taking technique suggested by Sönke Ahrens in How to Take Smart Notes.
While he doesn’t use the same terms, he encourages writing down and keeping fleeting notes as well as literature notes. (Keeping academic references would have been commonplace by this time.) He follows up with rewriting and expanding on the original note to create additional “explanations” and even “connections” (links) to create what Ahrens describes as permanent notes or which some would call evergreen notes.
Lichtenberg’s version calls for the permanent notes to be “separated and ordered” and while he may have kept them in book format himself, it’s easy to see from Konrad Gessner’s suggestion at the use of slips centuries before, that one could easily put their permanent notes on index cards (“separated”) and then number and index or categorize them (“ordered”).
The only serious missing piece of Luhmann’s version of a zettelkasten then are:
- the ideas of filing related ideas nearby to each other, though the idea of creating connections between notes is immediately adjacent to this, and
- his numbering system, which was broadly based on the popularity of Melvil Dewey’s decimal system and early 20th Century German filing practices (Aktenzeichen).
It may bear noticing that John Locke’s indexing system for commonplace books was suggested originally in French in 1685, and later in English in 1706. Given it’s popularity, it is not unlikely that Lichtenberg would have been aware of it.
Further, given that Lichtenberg’s very popular published waste books were known to have influenced Leo Tolstoy, Albert Einstein, Andre Breton, Friedrich Nietzsche, and Ludwig Wittgenstein, it would not be hard to imagine that Niklas Luhmann would have also been aware of them.
This short paragraph certainly says something interesting about the note taking methods of Lichtenberg’s time.
Lichtenberg, Georg Christoph. Georg Christoph Lichtenberg: Philosophical Writings. Edited and translated by Steven Tester. SUNY Series in Contemporary Continental Philosophy, 1.0. State University of New York Press, 2012
Lichtenberg, Georg Christoph (2000). The Waste Books. New York: New York Review Books Classics. ISBN 978-0940322509.)
- Did Lichtenberg number the entries in his own (original) waste books? This would be early evidence toward the practice of numbering notes for future reference. Based on this text, it’s obvious that the editor numbered the translated notes for this edition, were they also Lichtenberg’s numbering, or added later by other scholars/editors?
- Is there evidence that Lichtenberg knew of Locke’s indexing system? Did his waste books have an index?