I’ve no actual knowledge of how it works when a book is ghost written so please correct me if I’m wrong. But I think the way it’s generally done is the ghost doesn’t actually change what the author has said, nor can he or she make things up, or add untrue details into stories.
Or at least I’m fairly certain that would have been in the contract, especially for a book like this with so much riding on it...
So interviews will have been held, discussions had, recordings made, emails exchanged, and the ghost will write from that, in the subject’s own voice as much as possible.
Is that how it works?