I doubt very much if there is any religion on earth where all the adherents believe the same thing. In some this is tolerated, even encouraged, in others, like JWs of course, it's the opposite. Obviously JWs all believe the same core doctrines, (no trinity, no hell, no immortal spirit, these are the last days, the GB are semi-divine etc, etc), but there are bound to be differences on peripheral doctrine, because, as someone has already said, most of them don’t even know what the full set of doctrines is. And even is they did, they would still have to go back to the latest Watchtower on the subject to make sure their belief is up to date.