What would really be interesting would be to an estimate/analysis (similar to the above) of foreign-language JWs over the past 10 years, and try to see the rate of increase/decrease for English-speaking vs. non-English-speaking publishers.
I'd bet a nickel you'd see near double-digit growth among the foreign language groups, and a significant decrease (- 3%? - 5%?) per year for the English publishers.