As Tonus suggested, the math doesn’t work.
But of course, most JWs are incapable of anything resembling intelligent analysis so they just kind of shrug and ignore it.
The few attempts I’ve heard are a type “no true Scotsman” fallacy:
“Not everyone claiming to be a Christian really was a Christian, the apostasy was already working in the apostle Paul’s time, yada yada yada, hand wave here, misdirection there, why are you asking that question? Have you been reading apostate literature?”