I just googled 'overlapping generation' to double check whether it is a term in use anywhere else in the whole world. The only pages that came up were about economics. The Overlapping Generations Model. Note the 's' on the word generation. If they overlap, it cannot be 1 generation but 2 at least. Common sense really, just thought it was interesting.
Overlapping Generation (TM Watchtower Bible and Crap Society)