I don't see where you are going with all this. If JWs cared if 607 was correct, then secular proof is enough, since secular proof is required for 539, upon which 607 is based. Their belief is not based on logic, it is based on the want to believe regardless of logic.
"It is important to understand that in most Bible-based cults, although the member is aggressively taught doctrine, it is not the doctrine that holds him in the group. It is the sense that the group is God's true people, a feeling cultivated by techniques of mind control. Thus, to engage the cult member in a Biblical argument or discussion is often futile." Stephen Hassan, Releasing the Bonds p.145
JWs are not in it for the doctrine. They are in it for friends, for Jehovah, for paradise. No amount of Scripture will convince them that the Governing Body is wrong whilst they want to believe it.