They don't fudge the numbers because of what DagothUr just said.
The growing number of partakers explains the overlap doctrine and the overlap doctrine explains the growing number of partakers. The Borg loves circular doctrines.
What they will do is let this number grow for a period of time, with emphasis on the overlap doctrine. Then, they will put pressure on the rank and file AGAINST partaking, with the goal of reducing the numbers of new partakers each year. Shortly thereafter, the partaker death rate will once again pass the new partaker rate and the number will decline. THIS decline of the SECOND half of the overlapping generation will signal the imminence of the end.
I expect this turn to begin within the next decade, giving them a dozen or more years of declining partakers leading up to 2034