How do I get a complete list of items from the Google Books API?

Question

When I execute Volume: get searchor Volume: listusing the Google Books API, I do not get a complete list of objects. The API returns :

categories: [
    "Fiction / General"
],

And this shows an entry in Google Books :

Subjects
Fiction > Thrillers > Suspense

Fiction / Historical
Fiction / Literary
Fiction / Thrillers / Suspense

Has anyone come across this before and know how I can return this complete list of items?