I don't have a clue about the actual numbers, but I do think it was a mistake to return to the "generation" teaching after they effectively let it go in 1995. It was a way of admitting that the teaching was wrong, and they could still cling to 1914 as the year Christ quietly returned and began the last days. It would hurt them in terms of recruiting if they could not create the old sense of urgency, but the "generation" teaching was dead at that point.
Going back and redefining it was a way to imply that there is a deadline that can be counted, in the hopes of creating that old sense of urgency. But it's a complicated and messy concept, and you can no longer just say "the generation that saw these things is getting older" because (A)you already abandoned that idea and (B)everyone knows you can just extend it again. So you cannot create the urgency this way, but you also set off a lot of people's BS meters. There is only so much most people can take before the doubts become a real problem.