No-one can explain the Overlapping Generation teaching scripturally. it is the Emperor's new clothes ...
Basically JW's said (for about 45 years up until 1995) that the generation that saw 1914 would not pass away before Armageddy. Then there were a coupla changes and then since 2010 it's been "One generation Two groups."
So now if you were anointed in 1914 or before you are part of the first group. The second group overlaps and the second group must have been anointed before the last of the first group died.
David Splane "ex-Splanes" it by using Frederick Franz as an example of the first group because he was baptised in 1914 and died in 1992. So if you are anointed before about 1992 (as in started glugging the vino) you are in the second group.
Of course if you were a wine glugger after about 1992 then you are in a third group (tho they didn't say that!).
Of course there is no scripture or set of scriptures on heaven and earth that supports this utter nonsense which obviously came along because the crap they spout has run out of time.
So jw's deride Christendom for it's triune 3 in 1 trinity God but has its own triune trinity 3 in 1 generation ...