The 1963 All scripture is Inspired Book has the universe being created in 46,026 BCE. At that time they held to the view that each day was 7,000 years and then after 6 days(42,000 years) God rested (the Sabbath) after the 7th day(49,000 years) there would be the great Jubilee (the 1,000 year reign) after that everything would be back to the way it was in the beginning. This was modeled after the Jewish system and I believe this was a view held by other Bible commentators from before my time.
If the 1,000 year reign started in 1975 as expected this theory would have been right. If you were a studious Witness back then you could have expected the 1,000 year reign in 1975 based on this alone.