1975 wasn't presumed by the witnesses, it was presumed by some witnesses who based their life choices on rumors and hearsay rather than what was written, and they were weeded out. Which is why you should always confirm what you hear against what is written. Jesus clearly stated "no one knows the day or the hour".
Each creative day was followed by a life-impacting asteroid-like event, and science confirms that five such events have taken place. The 6th creative day was not followed by an impact, and this was where land animals and humans arose. Likely, the water plants, water animals and bacteria and millions of microscopic creatures which depend on a rhythm of day and night, and everything created on days 1-5 survived the 5th epoch-ending impact.
Simplified, there has been 5 events that extinguished all life on earth, marked by an x which signifies the end of that figurative creative day:
1x
2x
3x
4x
5x
6-humans created- vis-a-vis no new impact
7-rest day.
Likely the creative day needed to end with the impacts for some reason, but I can't fathom why. Some scientist might know why.
Whoever still believes the 7000 years lunacy is probably an "ancient astronaut theorist". Nothing happened on the jewish calendar at 1000, 2000, 3000, 4000, 5000, or 6000.
On a tangent, the nuclear blasts described in Bhagavad-Gita (which was read by oppenheimer, neils bohr, etc...) referred to the (highly intelligent if they are children of angels in human form) nephilim pitting humans against each other.
The big bang is now thought to have happened 13.8 billion years ago (likely the beginning of creative day #1), and the earth, about 4 billion years.
@lrkr states
But then, there was a sister in the engineering department in Brooklyn who was a geologist who told them that it was not possible to create oil, coal and other fossil fuels in 50,000 years. It takes much longer.
So, although some members of the GB didn't buy it- they quietly abandoned the 7000 year long approach and adopted the "a day is a time frame of unspecified length" teaching.
So just throw out all the 99.9% of good and get stumbled on the small details? The geologist was probably relating a relatively scientific discovery.
Ideas like this are like numerology and have been removed with good reason. OTOH Tesla was obsessed with 3, 6, and 9 but he clearly saw something normal people don't see.