The point about the census data is that they show Watchtower figures give a conservative estimate of their membership whereas other groups such as the Mormons grossly inflate their numbers. It seems that the Mormon church counts practically everybody who was ever baptised as a member regardless of whether they still have any contact with the church. That’s why you end up with the church claiming over a million members in Brazil but less than 300,000 describing themselves as Mormons in the census. For JWs it’s the other way round because their own count is far fewer than the census figure.
On one hand Watchtower is at a disadvantage financially because they discourage members from getting an education and a career and they don’t collect a tithe. On the other hand they discourage members from having children and instruct them to cut off contact with children if they leave the religion. As a result a considerable number of JWs leave their assets to the organisation in their will. Former Bethelites have confirmed the organisation receives a lot of money this way, especially now the baby boomer generation is dying off who accumulated property assets during the postwar period. Watchtower is not as rich as the Mormon church but they are probably comfortable within their current needs.