The Watchtower has forced a rather strange interpretation of the word "generation" in order to keep their doctrinal beliefs concerning the year 1914 consistent with the words of Jesus "This generation will not pass..."
However, the Watchtower's "overlapping" definition of the word generation is strange and unnatural to common use. According to the Watchtower, a grandfather, son, and grandson all living at the same time would make up a single generation. Ths does not make sense.
Here is a definition of the word generation.
"Generation, the entire body of individuals born and living at about the same time."
Now consider a definition of the word "Population."
"Population, the total of individuals occupying an area or making up a whole."
It seesm that the Watchtower has taken the concept of a "population over a time interval" and gven that meaning to the word "generation"
I do not know what the Koine Greek word is for "population" or if there is even such a word in the language.
Regardless, it is easy to see that the Watchtower is playing games with Biblical prophecy and interpretation by giving a new meaning to a simple word used by everyone.