I realize the position that every individual has a number of influences upon their actions and thoughts, perhaps we can't claim sole authorship, yet it will be claimed anyway.
Do we claim authorship of the cartoon that a child used to watch, upon penning a book deal detailing how the individual became successful, if the cartoon instilled goals that the individual achieved? There is a problem with authorship vs ownership here also and how they differ.
I think a compatibilist view is most close to the truth, it all depends on how you define free will and what degree you accept your every action is determined.
It isn't possible to ever know the full extent or infinity (or greater than infinity if not only measuring numbers).