That Eve was created and God's sabbath began less than a year after Adam's creation.
According to JW back then, the sixth creative day ended after the creation of Eve but because the Bible does not say when Eve was created, at first it was believed that Adam and Eve were created very close together so 1975 was the awaited date for something to happen. Later it was believed that Eve must have been created some years later after Adam and everyone waited for Eve to be created. What WT did in the publications back then was to show how it was logical for the Millennium to start 1000 years before the end of the 7th creative day. Everything added up and made sense although the publications did not actually declare that the end would come in 1975 but JW came to that conclusion from reading the printed information and it was believed by all although not actually stated in print. However, the faith of the JW about the Millennium does not rest upon whether or not its date can be extrapolated by WT. They still believe it will come.