When the Governing Body of Jehovah's Witnesses made chronology their focus they built on what others had done, said, asserted before them.
That is their data source.
The Adventists (William Miller in particular) used bible passages and also interpretations of certain perceived prophecies in books written by others--before him.
We are not talking FACTS. We are talking surmise, conjecture, guesswork and preconceived supposition.
None of these are facts! The Bible, as we all have come to regretfully acknowledge, is itself an estimate of things said and done which was first oral storytelling!
Nothing comes from nothing.
You can't be precise based on non-factual starting materials!
If you wanted to figure out what the surface area of the earth is--how would you do it?
By yourself, I mean.
A process based on previous work of others is not the same as starting from pure evidence.
Garbage in can lead to garbage out.
A cockroach in your salad can be removed with a fork. Do you continue eating having removed it?
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The process is the key to understanding!
Facts are the SAME for everybody.
Opinions about facts. . .distort those facts.
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1914 as the second coming of Jesus is not FACT. It is opinion. Opinion based on what? Storytelling interpreted and estimated into writing! Based on what? Belief in the story.
When a Jehovah's Witness sits down to "explain" how 1914 is contained in the Bible what are they really doing?
They are basing their process on a series of weaker and weaker connections none of which is provable, demonstrable or actual data.
If any part of any step is a false step the entire conclusion collapses into rubble.
How would this be possible to detect?
If any tentative estimate is used to create a prediction which does not take place in reality the initial premise is FALSE.
To make a long story short: Jehovah's Witnesses are not much more than an organization of people who can believe the Earth is flat by writing numbers on a sheet of paper while ignoring photos from space satellites.
Or, worse: an authoritarian regime who dominate the lives of unwitting believers who accept a long series of false premises as though they were facts.
The Book of Genesis says of the Flood that ‘… all the high hills that were under the whole heaven were covered…’ Taken literally, this seems to indicate that there were 10,000 to 20,000 feet of water on the surface of the earth, equivalent to more than half a billion cubic miles of liquid! Since, according to biblical accounts, it rained for forty days and forty nights, or at least for only 960 hours, the rain must have fallen at the rate of at least fifteen feet per hour, certainly enough to sink any aircraft carrier, much less an ark with thousands of animals on board.
– John Allen Paulos, Innumeracy
You see, when we can test our imagined "facts" against actual facts the results can be quite devasting to our false premises.