Each individual inventor may only assign the interest he or she holds; thus, assignment by one joint inventor renders the assignee a partial assignee. A partial assignee likewise may only assign the interest it holds; thus, assignment by a partial assignee renders a subsequent assignee a partial assignee. All parties having any portion of the ownership in the patent property must act together as a composite entity in patent matters before the Office.If it were any other way, any joint owner could easily "steal" the rights of his co-owners depriving them of any possibility of revenue. There is even case law prohibiting joint owners from granting exclusive licenses (rights that exclude other inventors from licensing) without the consent of all owners. Of course, joint owners can contradict these rules by a written agreement.
PS Dept. Your edition of our book may not be current (it's about 20 years old). The current version is entitled Profit From Your Idea: How to Make Smart Licensing Deals.