what was significant about 1914?
Seriously?
It was the date when war broke out in heaven and Satan and his angels were hurled into the vicinity of the earth, Jesus was crowned King and began ruling over a New Heavens and a New Earth. Have you no eyes, man?
O wait, I'm sorry. All that was invisible.
As for how long the WTB&TS can continue to use 1914 as a "Bible-based" anchor date, I think the answer is either "until time indefinite" or "as long as suckers are being born."
The date 1914 is essential to setting the date 2034. You haven't heard about 2034?
That's because the foundation-work for the date hasn't set yet; but 2034 is what you get when you add 1914 and 120, and 120 is the number of years that Noah spent as a special pioneer, selling his two prophetic clay tablet magazines, "Watch The Sky" and "Hepzibah." "Hepzibah" changed it's name twice, first to "Dehydration" and then to "Hey Now!"
It is rumored that in the creaky old Watchtower warehouse that still stands on Staten Island at the site of the old Bethel Farm and WBBR studios, the WTB&TS has a few of those old cuneiform tablets, but it has been forgotten if these are originals or reprints. From time-to-time one might show up on eBay at grossly inflated prices, often as ashtrays.
And although it sounds far-fetched, the magical date 2034 itself will spawn a host of dates by arithmetically mating with the "Bible-based" sacred integers 40 and 50 and their related factors.
...and THAT, dear friends, is THE REST of the story!