I remember the book that first "suggested" the 1975 date. It was entitled something like Life Everlasting in Freedom of the Sons of God. (Perhaps daughters of God do not have freedom?) I used to recall the page number, but have forgotten it. I also recall a Watchtower article entitled "Are You Looking Forward to 1975?" It was all the talk. People were postponing health care and dental work. People were quitting good jobs and becoming handymen to have more time for the preaching work. The Truth that Leads to Eternal Life (the "Truth book") was published about 1968, and we were instructed to study with people only 6 months and press them to make a decision within that time frame because the end was SO CLOSE!
They can't fool anyone who participated in that collective madness, particularly if we still have a working memory.
I posted this information for those who were not there in the pre-1975 hysteria so they could have a frame of reference if anything ever came up about this issue.
Letting go of our delusions is one of the most painful human experiences, but so worth it!