Good question Magnum!
I agree with you Millie 210 that Jewish scholar friend of Freddie Franz was important grist to his Biblical mill. I saw and heard Franz when in his nineties at close quarters while working as a consultant at UK Bethel. An inoffensive even self deprecating man, his role in influencing the course of the JW org through the 20th century was I believe of prime importance.
He had the role of being the back room theological boffin as I understood from Bethelites. He was the right hand man of the more business minded Knorr who would defer to Franz on points of “learned” doctrine. Remember for example that he told president Knorr that a governing body was not scriptural –as I understand.
So Franz had smatterings of Greek and a fair understanding of the contents of the Bible which he expounded with certainty on the advent of Christ in very specifically his own day. He was baptized around 1914 and he saw his role elevated as God’s spokesman to declare 1975 as the fitting end of the (fictitious) six thousand years of the final seven, with one thousand to go for the final testing. All ideas clearly possible within the jumble of Bible texts.
Like Russell, he felt he was certain about the revelation of his end-times doctrine and along with his connections at the top of the organisation this gave him the authority and platform to fully promote his delusions. For half a century this contributed to the Franz outlook on all things Watchtower.
What Franz had was not logic... he always used non-sequiturs and wild but spiritually credible assumptions. His mindset and even his oratory I think, had echoes of Millerite preaching and date setting methods using faith in the Bible and a language of absolute certainty. If God is right and he cannot lie; therefore such and such. . .
His teachings are now shown to be false and played down by the GB but his oratory style declaring absolute certainties on divine assumptions remains the most effective way of bamboozling the flock.
So without FF who knows! but perhaps someone else would have taken up a similar cues to mislead JWs.