"Levels by" categories
The 4 "Levels by" categories need 9 intermediate-level categories to be created and the 60 existing leaf-level categories to have the relevant parent category added. Since updating 60+ category pages will be exhausting and the "Add category" button at the page bottom doesn't always seem to be co-operating, I've not done that. As a workaround, I've simply linked the existing categories by means of hyperlinks (which was only 4 pages of work that could be easily filled in using a script). Hopefully, someone else can eventually update these categories and then get rid of these links.