The J.W. org., along with many other sects, ignores the long agreed meaning of "Genea" or Generation, in Jesus words in Matthew and Luke, Vines Expository Dictionary explains that it means what we mean by the word in most instances, a group of people who inhabit together a time that lasts 30 or 40 years, and then the next generation comes along, Vines also explains that it does NOT mean "a time period of indeterminate length".
By using Eisegesis, reading in to a Text what is NOT there, J.W. org. twist the obvious and plain meaning of Jesus words when he said " this generation", he meant those people standing and listening to him, who were of an age with himself.
His prediction failed, but to look for a later fulfillment of a prediction that has already failed in a major feature of it is plain silly.