westibilly11: If so, why would they? What would be their motive?
There is no shortage of people who have predicted the date of the end over the past two thousand years. I think that, for most of them, the motive was a sincere desire to know. The early predictions of men like Russell and Rutherford were probably formed from a desire for it to happen, a desire to see it, and at least in part the realization that it would get people's interest piqued.
Surely, the WTS could not ignore the growth that occurred during the late 60s and early 70s after Franz wrote about the 1975 date. By this time, bitter experience had led them to provide the occasional disclaimer and not sound quite as certain as the early leadership. And if the words used just so happen to mislead people into staying, well... those increases sure did look good.