Luhmann viewed his Zettelkasten as a tool to help him stumble upon unexpected but related information at the time he needed the information. For that the links don’t need to be perfect.
Think of it this way. When you look something up on Google, it would be nice if the perfect result you need was always the first search result. But at the end it really doesn’t matter that much if the perfect result is the third, fifth or tenth result. As long as you can find it when you’re looking for it (even when you don’t know what exactly you’re looking for), Google is doing its job.
It’s the same with the Zettelkasten. As long as the links are set up in a way that allows you to find the unexpected surprising information when you need it, the Zettelkasten is doing its job. For that the links don’t need to be perfect.
Another way to think about it is as a road system in a country. You start out in city A and the perfect information is located in city D, but you don’t know that. It would be really nice if there was a direct road from A to D. But if there isn’t, it’s not too much of a problem. You just start out in A and begin your road trip. You visit B, then C, and then (what a surprise!) you’ve found this perfect place that is D. You unexpectedly found D and now know that D is what you were looking for. As long as D is reachable without too much effort from A, the road system is useful.
And so it is with your Zettelkasten. As long as everything is interconnected in such a way that relevant information can be found without too much effort, the notes are sufficiently interconnected. You don’t need to worry about having everything linked in a perfect way. Moreover, remember that the Zettelkasten improves organically. If you start out in A and then later find out that D is perfectly related, you just add a link from A to D at that point in time.
Hope this helps! Happy Zettelkasting ;-)