You’re right, if the guy with the rings who killed her father is Bill, then that would be a very interesting plot twist. Just because there’s nothing mentioned in the volume 2 script doesn’t mean it’s not going to be in the movie. It is only an early draft of the script and a lot of things changed. For example when Bill tells the story of Pai Mei, originally it was suppose to be in the Jeep, now it’s at a campfire.
