What I remember was when '75 came around the Society started saying that there might be a difference between the end of 6,000 years of God's "rest day" and 6,000 years since Adam's creation. So, there could be a few weeks or months difference from when Adam was created and when God's "rest day" began right after the creation of Eve. So, many of us kept in eager expectation of the Great Tribulation starting even as '75 passed because we still believed the 6,000 years of God's "rest day" was almost over. Where did we get this info? From the Watchtower Society itself!
From the May 1, 1975 Watchtower, p. 285:
Another speaker, F. W. Franz, the Society’s vice-president, forcefully impressed on the audience the urgency of the Christian preaching work. He stressed that, according to dependable Bible chronology, 6,000 years of human history will end this coming September according to the lunar calendar. This coincides with a time when “the human species [is] about to starve itself to death,” as well as its being faced with poisoning by pollution and destruction by nuclear weapons. Franz added: “There’s no basis for believing that mankind, faced with what it now faces, can exist for the seventh thousand-year period” under the present system of things.
Does this mean that we know exactly when God will destroy this old system and establish a new one? Franz showed that we do not, for we do not know how short was the time interval between Adam’s creation and the creation of Eve, at which point God’s rest day of seven thousand years began. (Heb. 4:3, 4) But, he pointed out, “we should not think that this year of 1975 is of no significance to us,” for the Bible proves that Jehovah is “the greatest chronologist” and “we have the anchor date, 1914, marking the end of the Gentile Times.” So, he continued, “we are filled with anticipation for the near future, for our generation.”—Matt. 24:34.
(Makes me wonder how long Adam was in the garden alone before Eve was created?)
The point is, it was the Watchtower Society who started the excitement about 1975, starting in 1966 with the release of the book Life Everlasting in Freedom of the Sons of God. They fanned the flames of excitement many times during that era. Especially as we neared 1975 there were a few attempts to suggest caution (perhaps some at the top realized there could be a real problem is nothing happened in 1975), but this was not a case of a few JWs getting this idea on their own. It all came from the Watchtower Society!