Since the membership accounting is based on turning in "time", there is lots of room for fudging. This is done from Joe/Jane publisher, all the way to the top.
First of all, consider that members are constantly coerced to actually turn in time. There is a negative social stigma associated with not doing so, in the form of being labeled "irregular", or "inactive". Nobody wants those labels, if they care about their status in the congregation. There is no telling how many individual members turn in time that have zero desire to do so.
Secondly, the organization is not transparent in how it performs the accounting to begin with. What is a "publisher" really? Must they be baptized to be counted? Do they count heads when convenient? There are so many things that can be "adjusted" behind the scenes, that numbers can be spun positive for some time just by changing what is being counted.
Figures don't lie, but liars can figure.
d4g