From Authorgraph’s recent newsletter:
Multi-author support is finally here!
This has been the most popular feature request from authors and I’m happy to announce that it is available today.
The process of claiming a book by additional authors is exactly the same as for a single author. Simply go to Add your books and enter the ASIN for the book you’d like to claim. A multi-authored book will now appear on the author pages for each of the authors and readers can choose to receive an Authorgraph from one or all of them.