7 - Structuring for Retrieval - An important aspect of the zettelkasten to understand is that Luhmann’s method of structure facilitated his end use case (writing). He created sequences of notes (1 - 1a -1b - 1c), which allowed him to easily pull out all the notes on a given topic when he needed them. Otherwise he could have just used a numbered list for notes (1, 2, 3, 4, 5, new note 6) where the newest note is just the highest number.
What all this suggests is that you should keep in mind how you plan on using your zettelkasten when you start to add layers of structure. Do you plan on using it for writing like Luhmann did? Or do you strictly want to use it as a reference system? Or are you using it to build external models, that once finished, become mental models?