What’s the difference between adding a “label” and creating a separate product when selling print books directly?

If you’re a PRO tier subscriber, you can sell print books directly. You can set up these sales in the “Sell Directly” tab of your book in the editor. The “Label” field indicates the particular format of a book. If you have a completely different book (with a different title), you should set up a separate product in the Books section of your editor.