I've noticed that this is a frequent discussion point since joining this Discord server. In a set of notes that changes often I don't think you can ever consider your hierarchy complete. I find that having to move notes down another level is actually a sign that I've learned more, and the act of reviewing them probably helps with recollection. Don't be scared of losing notes in the hierarchy, I guess, lookup, backlinks and a bit of find in files can always find your notes