Here's what Ray Franz wrote in his second book:
In a little more than a decade, the only persons born on or before
1914 will be those who are centenarians. As documented in
Crisis of Conscience, despite the confident-sounding statements in
Watch Tower publications, a considerable number of Governing
Body members had long recognized that the traditional teaching
about “this generation” was proving more and more tenuous.
There is no other explanation for the fact that in 1980 the members
of the Chairman’s Committee drew up and presented a document
which, if its reasoning had been accepted, would have placed
the start of “this generation”—not in 1914—but in 1957, when the
Soviet Union launched its first Sputnik!
Finally the teaching became so obviously untenable that a major
change in the definition of “this generation” was made, applying it to
“the peoples of earth who see the sign of Christ's presence but fail to
mend their ways.” The time factor thereby virtually disappears!
A similar pattern of shifting definitions can be found in the
Watch Tower publications’ efforts at fixing 1914 as the time when
a unique worldwide “sign” appeared, related to war, famine, earthquake
and pestilence.