I always get an interesting reaction when I ask "how long after Jesus said this, did Jerusalem fall?" First their eyes go wide open. I say "It was only 37 years later. So the generation that Jesus was taking about, wasn't overlapping."
Way back when, the organization used to make a big thing about Christendom using the word Trinity. "The word Trinity is not in the Bible!" Obviously, they couldn't be following the bible. But what are they doing now? Using the word "overlapping" just like the others used "Trinity" to prove their version of teaching.
When you think about it, they have 3 overlapping generations and there are 3 in one. Three is a popular number I guess.