The credit goes to Luhmann. Ahrens wrote a book about Luhmann's system, but Ahrens' book was more about the practical side of study habits and the nature of knowledge as much as it was about the practical side of actually using a zettelkasten.
My Obsidian Vault setup: https://bryanhogan.com/blog/obsidian-vault
All posts about Obsidian: https://bryanhogan.com/tags/obsidian
Maybe this helps?
Edit: Upon a quick scan, this looks more like what I learned as "Linking Your Thinking", which resonates way more with me than a strict Zettelkasten format where you try to arrange notes linearly to match some artificial constraint.
And I think that's a good thing, just not how Ahrens described Zettelkasten.