One thing to keep in mind regarding the stats, particularly in the wealthier and/or Western nations, the ones with a -1% to +1% growth rate:
Virtually all the baptisms are via children of established publishers, or from immigrants. For example, in the US, fully 1/4 (over 250,000) of the publishers are in Spanish-speaking congregations. In areas where there is a large immigration rate, it is not uncommon for some pioneers to have (literally) 8 or 10 studies, and to have 1 or 2 of those studies progress to baptism per year. In some larger metropolitan areas with a large Spanish-speaking immigration rate, new Spanish-speaking congregations are formed every 18-24 months. Based on my observations, I would not be surprised if the Spanish-speaking publisher growth rate in the US is 10% or more per year.
If the Spanish-speakers are growing so rapidly, and the overall growth rate in the US is flat, what does that mean about the 750,000 English-speaking JWs in the US? The number is dropping precipitously, perhaps more like -2% or -3%.
And, any success in other Western/wealthy countries is, I strongly suspect, due to large increases in the immigrant population and success in witnessing to them. In Western Europe, there are numerous immigrants from Africa, Turkey, the Far East...etc. And in Spain, there are numerous immigrants from Latin America.
Immigrants to a wealthier nation are going to be on the lowest rung of the socio-economic ladder. They likely moved due to horrific economic or political pressures, and perhaps arrived with literally no more than the clothes on their backs. They live in hovels, or 12 to an one-bedroom apartment, and whatever meager money they earn is sent back to family left behind.
Now here comes Joe and Susie Pioneer to their door, with glossy brochures promising them (comparitive) mansions and good health and freedom from all problems. "Great, where do I sign up?"
If not for the massive amounts of immigration in the past decade or 2, you'd see even bigger growth in 3rd world countries, and rates of -2% to -5% in Western countries.