I would not trust any figures the WT publishes. They are lying sacks of shit. Anything they publish has an agenda. They are trying to show growth and not let on that there is a big exodus happening. Selling valuable properties, moving to the boonies, dissolving congregations, selling Kingdom Halls, robbing congregations of their accounts and tons of bad publicity over child molestation lawsuits.
When have these guys ever been honest they only honestly print facts when it furthers their cause.
By giving a basic over all figure for the work world wide makes it easier to fudge the figures as less people know they fudged them.
Any growth they report I'm sure was inflated by the those who compiled it and suggestions from the GB.