Hi MicaSmith I can tell you WHY the WT came up with the overlapping generation in 2010.
It is because it suits their purpose. The purpose of keeping followers hanging on and justifying their existence as leaders.
The previous explanations of the generation were so obviously wrong that they had to change it for fear of even more people querying their explanation.
The explanation that got everyone who is a witness hooked was the one that told us that the generation that "saw 1914" (originally "with understanding" e.g a minimum age of ten - fifteen years old in 1914; but the "with understanding" got dropped as time ran out) would not pass away.
Even when this explanation was dropped in 1995, some folk clung to the hope that it was still true by telling themselves that a few million round the globe who "saw" 1914 would by no means pass away.
Now we live at a time where those born in 1914 are 102 years old it is obvious to virtually everyone that the old explanation cannot be sustained any longer. Hence the latest new, new one! (Several explanations since 1995)
edited to add: Actually Xanthippe, although the long held explanation was dropped in 1995 the overlapping crap wasn't brought out until 2010. There were two or three other crappy explanations in between!