I asked this when I was first trying to wrap my head around the fact that the JWs/WT was not the "truth".
And after all this time, I can say that...I'm still not sure. I think maybe a couple of them have deluded themselves into believing it but I can't see that the entire body believes all of it.
Those that don't believe the entire thing are in too good of a position to give it all up. They don't have to work, they're expenses are covered and they have power and control over millions.