The thing is, for an ISBN, that is one edition, by one publisher and one can easily have the same text under 3 different ISBNs from one publisher (hardcover, tr

The thing is, for an ISBN, that is one edition, by one publisher and one can easily have the same text under 3 different ISBNs from one publisher (hardcover, trade paperback, mass-market paperback). I count 80+ editions of J.R.R. Tolkien's _The Hobbit_ at: https://tolkienlibrary.com/booksbytolkien/hobbit/editions.php https://tolkienlibrary.com/booksbytolkien/hobbit/editions.ph... granted some predate ISBNs, one is the 3D pop-up version, so not a traditional text, and so forth, but filtering by ISBN will _not_ filter out duplicates. There is also the problem of the same work being published under multiple titles (and also ISBNs) --- Hal Clement's _Small Changes_ was re-published as _Space Lash_ and that short story collection is now collected in: https://www.goodreads.com/book/show/939760.Music_of_Many_Spheres https://www.goodreads.com/book/show/939760.Music_of_Many_Sph... along with others.