It there anywhere to get those numbers (Without a yearbook or where ever they publish it now)? It would be helpful. The WT numbers are quite reliable. Rodney Stark has analyzed them and said their not inflated. They also match with third party surveys. This "honesty" will be quite interesting if/when their numbers in the USA start declining.
I guess they could pad by incorporating other areas into the USA, but that will just hurt them the year after because of the unreproducible spike in growth.
On the 'charismatic leader' front, this won't happen until after a the GB is in panic mode. People don't give up power unless they think they will lose it anyway if they don't act. So, I think speculating about this leader is a bit premature.