While I am a big proponent of finding out what the bibles means by comparing separate texts, I have to admit that it is not possible to compare the meaning of "generation" by simply looking at what one generation understood as "generation" compared to what a much later generation understood by "generation". In other words, whatever length of time a generation was in the times of Abraham, is not necessarily the same during the times of Moises or Jesus. In either case, it is understandable that the people of whom each one of us considers to be of the same "generation" as us, vary in age, experience and the like. A generation can be grouped by chronological age as well as having experienced a certain dramatic event or time in history.
With that in mind, two people can be of the same generation that saw men walk on the moon and yet, as far as age is concerned, they could be of two totally separated generations (father and son for example). In this case you do have an "overlap" but at least, both generations have witnessed the same event. When it comes to this there is no escape to the rule that, whichever generation must be alive before the Big A, overlapping with another one or not, it must have witnessed the event in order to qualify to fulfill the prophecy.
Unfortunately, even stretching the definition isn't enough at this point. How many anointed witnesses that overlap with the 1914 generation are still alive? Not many. The "overlap", even if it was correct, is no overlap anymore.