My own implementation of a Zettelkasten does not make a distinction between continuing topics (or weiterführende Zettel) and branching ones (also called ergänzende Zettel). I did not think that this was important for two reasons
1. an electronic topic or Zettel can be as long as I want it to be, and
2. it does not seem to be really important for the praxis of taking note to differentiate between supplementation or branching and linear continuation. For one thing, you can always add new stuff to any particular topic as you need to. No acrobatics in numbering seem necessary. And linear sequence is in some sense just as much a link as is branching off. [[Kladde|Heft]]
But what if I wanted to make such a distinction between different sequences? It is, of course possible. Linear sequences can be indicated by either linking the end of one topic to the topic that follows. (You could use something like [[following topic|blah, blah, blah]]. You could, of course, also use the name of the topic followed by a number from 1 to n. And you could reserve textual links for branching topics.
There are other ways of doing this, as with properties, for instance.
The only question is whether it would be worth my while. I am not sure it is, but I am willing to be convinced that it is.
1. Luhmann's numbering system represented, as it were, the exoskeleton of the Zettelkasten. A wiki database does not need it, as any entry in it represents a fixed location in a database. Textual implementations, like nvALT and other do not have this advantage. If you rename either the link or the linked item, the connection is broken. They might need an exoskeleton as well.