Hooray For Diffendoofer Day by Dr. Seuss
Hardcover picture book is Like New. Dr. Seuss was unable to finish this story before his death. Years later an editor reached out to Caldecott winner Lane Smith to add illustrations and poet Jack Prelutsky to add more text. The back of the book has a section filled with reproductions of the sketches and text found in the file Theodor Seuss Geisel was working from.