In talks and in print, the Society never said that Armageddon WAS coming in 1975. They said, it would be extremely appropriate, marvelous things may happen, and if things seemed delayed maybe it could be because the 6000 years didn't start till Eve was created, and we don't know how long from the time Adam was created to when Eve was created.
Official talks given by Fred Franz discusses this further (the author of the book "Life Everlasting in the freedom of the Sons of God", which started all the excitement about 1975):
There's also a talk Charles Sinutko (a circuit overseer whose life experience was in the August 22, 2004 Awake pg. 19) was evidently reading too much into the Society's statements about 1975. This was one of the most forceful expressions I've heard regarding 1975, but it is not official. (I thought this was also on archive.org, but I can't find a link to it. Anyone have a current link?) From the sounds of people's experiences here, the excitement was stronger in some circuits/congregations than in others.
On a somewhat related, and possible more honest note, in 1925 when Rutherford's predictions never happened, he admitted to the bethel family "I made an ass of myself" (w84 10/1 pg. 24 footnote).
@Spade/SuperSpook/Maze et al.
Jehovah's Witnesses simply reflected what's contained in the Bible and associated means of measuring where we are in the stream of time.
If Fred Franz hadn't conjured up the 1975 idea, there would be about ZERO Jehovah's Witnesses who would have had the means or influence to come up with such a thing and spread their idea. Jehovah's Witnesses got that idea from an organization that teaches truth (or at least speculates truth in this case).
Your mother was right when she said that only the spiritually weak left the organization. Jehovah's Witnesses that are spiritually strong don't base their spiritual endeavors on a pivotal date for the end of this system of things.
And directly related to the point above, Jehovah's Witnesses as individuals would not be fixated on a "pivotal date" unless it came from the organization. There have been no issues regarding "pivotal dates" in the past 36 years because the Organization has stopped guessing dates (which also coincides with the full transition to the Governing Body arrangement in 1976, whereby one person's doctrinal ideas can no longer make it into print unless approved by the body).