On this broader subject, see the long-running thread re: organising academic stuff.
This speaks to this ‘organising academic classes’ issue. In your example there you wouldn’t have an entire category dedicated to 31 English 101. This remains an issue to be solved; ref. other thread.
It’s been a looooonnng time since I’ve studied anything but my gut feel is that this would be okay. The more I do this the more I expand what a single ID can contain.
This rule has been relaxed to ‘avoid creating subfolders’. In some situations I now think that subfolders are fine.