The other C&H item I found is "Dear Mr. Watterson," a 2013 documentary that follows the same template as the book: since we can't talk to the man himself, let's interview other cartoonists, let's visit Chagrin Falls, let's look at some original art in the Cartoon Museum. Unlike the book, lots of examples of his art shown. Unlike the book, Bill's parents aren't interviewed.
Nevin Martell, the author of the book, is featured prominently. Seems fitting somehow that a movie about a recluse should turn in on itself this way.
An odd -- and possibly appropriate -- feature of the DVD is that there are no menus. You put the DVD in and it starts playing. When it's over it starts playing again. There are no "extras" or bonus features or chapters. It just is what it is.