I'm guessing that "shop filters" are very generic-looking, just painted simple or plain with minimal markings. Many filter manufacturers have their own versions of these. They might consolidate applications into fewer units too, such as eliminating (using Fram numbers) 7317 filters with 6607 - the 6607 will fit anywhere a 7317 fits and the slightly smaller size is a non-factor when it comes to capacity.
By the time you pay shipping, why not just use a Supertech, Fram PH, etc ?