One mistake in the original article: "Subtracting the increase in average publishers from the number baptised each year can be used to determine the number of Jehovah's Witnesses that leave each year. "
And that is a crucial mistake, for the simple reason that one does not have to be baptised to be included as a publisher. Because of this, it is impossible to produce statistics like the ones shown. There is no way knowing whether an unbaptised person starts publishing, stops, starts again etc. If you had to be baptised, it would be easy, but now it is close to impossible. You would have to know the exact number of the publishers that are baptised in order to do the math.