I feel there is a "biblical basis" for extending the horizon beyond what you have said.
(Note to the WATCHTOWER BIBLE & TRACT SOCIETY - this "new light" is copyright 2010 by Nathan Natas.)
The longest overlapping generation in the Bible is Methuselah and his great-grandson Shem. Together their two lives spanned 1,469 years.
People will protest, "but folks today don't live for five hundred or more years!" Clearly, that argument is biblically irrelevant, since Jesus said that the last days would be like the days of Noah.
Methuselah was a man approved by Jehovah God. He foreshadowed the "early" anointed of these "last days in that he (Methuselah) did not live beyond the expression of Jehovah's righteous wrath upon THAT generation. That expression of wrath was the FLOOD.
Shem, however, foreshadowed the "late anointed" of these last days. Shem DID survive the expression of Jehovah's wrath upon an ungodly world.
Likewise, in today's "last generation" spanning 1,469 years, there will be some anointed who have the privilege of standing with Jehovah at the beginning of the last days (1914) and other anointed who will be alive when the "generation" comes to a close in the year 3383 CE. Those anointed will not have the joy of being present at the beginning of Jehovah's work during the last days, but will have the privilege of surviving Jehovah's "day of wrath" at Armageddon and providing counsel and guidance to non-anointed human who also survive that great day.
See how easy it is? If even a lowly apostate like myself can whip up a turd sandwich like this so easily, the sociopaths in charge of the WATCHTOWER can do the same. Just be warned, WATCHTOWER and other parasitic meta-physicians - this particular line of crap is copyrighted by me, Nathan Natas. Don't plagiarize me. Write your own crap.