Sometime around 1972 Fred Franz, the WTBTS master chronologist, determined that his date of 1975 was off by a year and that the real date was 1974. According to the account written by Ray Franz in _Crisis of Conscience_, the governing body decided to suppress this because of the "unsettling effect" it would have on the brothers. So it never made it into the literature.
But, it did make it into the rumor mill as I heard about it back then from one of my gossip-loving JW relatives. It wasn't until about ten years later that I made the connection when I read _Crisis of Conscience_. I believe it was in the same chapter that the then WTBTS president Knorr expressed his doubts, not just about 1975, but also about 1914. Of course, if a rank and file JW did such, the judicial boot would soon follow.
Perhaps Knorr, like Rutherford before him, was feeling the end of life coming on and this had a bearing on his decisions. Had Knorr been diagnosed with terminal cancer at that time? Perhaps that made him a little doubtful on how things were going. This was different from Rutherford, also a terminal cancer victim, who probably was motivated by his condition in his last couple of years as he promoted the idea that World War II would end in the Big A and he would make it through.
When then president Fred Franz met his long delayed end in late 1992, I'm sure that the revisions to his precious 1914 generation doctrine started almost immediately thereafter. Maybe the plans were already in place, but were held up because of the opposition of Fred and his sycophants on the governing body.
So, expect more "new light" when Milton Henschel bites the dust or is eased out of active participation. With the organizational changes of last year, the latter may have already started.