They stated many many times that it is the Creator's promise that the generation that saw the events of 1914 would not pass away until there is a new world.
"Was Jesus using the word 'generation' in a symbolic way? No, we should not say that the word “generation” here has a symbolic meaning....The “generation” of Matthew 24:34 includes persons alive at the time that the war in heaven began in 1914....Members of that generation will see the end of this world” (Awake!, September 22, 1962, p.27).
Every two weeks for almost 5 43 years — from 1952 to 1995 — the Watchtower Society’s “Awake!” magazine’s masthead use to read,
“Why Awake is Published— Awake is for the enlightenment of the entire family... Most important, this magazine builds confidence in the Creator’s promise of a peaceful and secure new world before the generation that saw the events of 1914 passes away” (Awake!, October 22, 1995).
That sounds like a false prophecy, in the name of God, to me.