I'll try ...
Up until 1995 and especially after the 1975 debacle "The Generation" was understood as those aged between about 70 and 80 - that saw 1914 (with understanding) and would not pass away before Armaggeddy.
When it was becoming obvious that the generation WAS passing away the age of understanding not-so-subtly dropped from 15 to 10 to babies.
By 1995 the gig was up as we were now 81 years from 1914.
So the definition of "The Generation" was changed a few times between then and 2010 - see jw.facts for details - when the infamous overlapping generations arrived and more recently the "Ex-Splaned" chart shows how it works. (Using F.W.F. and causing WTF? from many on this and other forums.)