But do most Witnesses know what they believe in??
No. A few years ago two men (had that look that made me think elders) came to my door. I've moved several times so they had no idea I'm an XJW. They introduced themselves and said they were JW's. I stopped them right there and told them as a Christian I can't follow a group that doesn't accept Jesus as mediator for all people. He said I was mislead, they believe he is.
Me: when did that change?
Them: We've always believed that.
Me: There are two QFR articles in the 1989 Watchtower that say differently. Why don't you check on that and come back, I'd be interested in hearing about it.
Never saw them again. I suspect there are other issues where they don't know what their own religion teaches.