He definitely uses an editor and gives them (I think there are 2 of them) chunks of the book as he finishes them. They then make suggestions and he will go back and revise chapters if needed. My understanding is that, for some chapters, there is a lot of back and forth before they get to the final version. But, some percentage of TWOW is completely finished and ready to go to the publisher. I don't think he submits anything to the publisher until it is 100% complete. That would probably result in too many eyes having access to parts of the book for an extended period of time (potential leaks).