In response to the OP, the Watchtower of July 15, 1976, p. 437 gave us the Adam-Eve creation gap explanation for why nothing happened in 1975. After 9 years of stressing how close the end might be, they gave it an indefinite expansion:
"What, then, does this mean? Simply this: That these factors, and the possibilities for which they allow, prevent us from saying with any positiveness how much time elapsed between Adam’s creation and that of the first woman. We do not know whether it was a brief time such as a month or a few months, a year or even more. But whatever time elapsed would have to be added to the time that has passed since Adam’s creation in order for us to know how far along we are within God’s seventh “day,” his grand day of rest. So our having advanced six thousand years from the start of human existence is one thing. Advancing six thousand years into God’s seventh creative “day” is quite another. And we do not know just how far along in the stream of time we are in this regard."
A 1974 Kingdom Ministry had praised JWs who sold houses and property in
order to pioneer for chosing "a fine way to spend the short time
remaining before the wicked world’s end." But now the July 15, 1976 Watchtower (p. 441) blamed those same sheep for not taking care of their families' necessities:
"But it is not advisable for us to set our sights on a certain date, neglecting everyday things we would ordinarily care for as, such as things that we and our families really need. We may be forgetting that, when the “day” comes, it will not change the principle that Christians must at all times take care of all their responsibilities. If anyone has been disappointed through not following this line of thought, he should now concentrate on adjusting his viewpoint, seeing that it was not the word of God that failed or deceived him and brought disappointment, but that his own understanding was based on wrong premises."
By 1980, it was becoming clear that the Adam-Eve creation gap explanation was wearing awfully thin, and blaming the sheep was drawing a growing backlash of anger and contributing to a decline of membership and activity. Finally, nearly 4 years later on March 15, 1980, the Watchtower stated on pp. 17-18:
"In modern times such eagerness, commendable in itself, has led to attempts at setting dates for the desired liberation from the suffering and troubles that are the lot of persons throughout the earth. With the appearance of the book Life Everlasting—in Freedom of the Sons of God, and its comments as to how appropriate it would be for the millennial reign of Christ to parallel the seventh millennium of man’s existence, considerable expectation was aroused regarding the year 1975. There were statements made then, and thereafter, stressing that this was only a possibility. Unfortunately, however, along with such cautionary information, there were other statements published that implied that such realization of hopes by that year was more of a probability than a mere possibility. It is to be regretted that these latter statements apparently overshadowed the cautionary ones and contributed to a buildup of the expectation already initiated.
"In its issue of July 15, 1976, The Watchtower, commenting on the
inadvisability of setting our sights on a certain date, stated: “If
anyone has been disappointed through not following this line of thought,
he should now concentrate on adjusting his viewpoint, seeing that it
was not the word of God that failed or deceived him and brought
disappointment, but that his own understanding was based on wrong
premises.” In saying “anyone,” The Watchtower included all disappointed
ones of Jehovah’s Witnesses, hence including persons having to do with
the publication of the information that contributed to the buildup of
hopes centered on that date."
I believe that's as close as the GB ever came to an apology. Notice that they only admitted that WT publications implied that the 1975 expectation was more a probability than a possibility and so "contributed to the buildup."
No mention is made of the fact that if you didn't believe in the 1975 date at the time and promote the imminence of Armageddon as often as you could, you were considered spiritually weak or much worse...
I'm not aware that the GB ever retracted the Adam-Eve gap explanation. It's been 42 years now -- quite a gap!
They hoped 1975 would fade from memory.
Now they are presenting the JWs' wrong expectations and disappointment as a test of faith to show that JWs' loyalty is to Jehovah, not a date. The implication, of course, is that if you are still bothered by the 1975 failure (or the failure of another other WT dates) you aren't being loyal to Jehovah. Once again, it's your fault, not theirs.
The fact that they are still discussing this shows that the false prophecy issue (though the WT would never call it that, of course) is still troubling JWs or at least causing them trouble when talking with outsiders.