If you wanted it to appear in the subcategories, then every one of those sources you have listed would have to have [[Category: Sources-Rowley, Rowley Name Study]] on them. As you cannot do that (some of them are external books) it can't be a category page showing a group of categorised items.
Category page has subcategories on it.
Subcategories have categorised items within them
What you have there is a list of useful books, which belongs on a freespace page.