It's true that the WT has taught that all Christians between 100 AD and the early 20th century were anointed. But it's also the case that they reckon that most of those who professed to be Christians were false Christians in that period. So their numbers work in their own terms.
By the way, since they dropped the 1935 date as the cut off for anointed, I am not sure if they do still definitely teach that all Christians between the first century and the twentieth century were anointed. It's certainly what they used to teach when they had the 1935 date. At the moment what they teach appears a bit ambiguous. Maybe they will "clarify" at some point, especially if the numbers look increasingly incredible.,