Lying about the numbers would take some corroboration. I think that GB members and the others who assist them with the writing of their articles are aware of problems, but don't directly think they are liars. It's kind of like a state government saying that "profits" from the lottery go to schools. Some of them do, some of them do. So it's not a lie to omit other places the money goes.
Watchtower leaders think that it is okay to mislead the members as long as there is "truth" within what they say. I think that they have manipulated numbers enough to make the "growth" of the last several years seem true in their minds. For some reason, they think that the USA should have growth so they have consolidated lands that used to be counted separately, they have allowed the 15-minute publishers, they have allowed both parents to count a study with their children so that even an inactive couple could claim some time.
They will probably cross the line of truth/lying sometime soon about this, but first they will have to either convince themselves that they are telling "truth" or that deliberate misleading without truth is necessary. If they have a couple of years of no-growth no matter how they manipulate the numbers, I see them flipping to counting people differently by using meeting attendance and phone-in numbers will be included, then they will start counting website hits somehow.