Actually, the society did make a kinda, sorta back-handed apology for the mess made by 1975. Ray Franz mentioned it in Crisis of Conscience, Faced with declining numbers after 1975 the society voted to issue at least some acknowledgement of its error. This was done in the 3-15-80 Watchtower, cleverly hidden in an article entitled "Choosing the Best Way of Life" and in a convention talk with the same title:
Watchtower 3/15/80 Choosing the Best Way of Life
"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 LifeEverlasting—inFreedomoftheSonsofGod, 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"
1980 Yearbook of Jehovah's Witneses- Pages 30-31
"The brothers also appreciated the candor of this same talk, [Choosing the Best Way of Life] which acknowledged the Society’s responsibility for some of the disappointment a number felt regarding 1975"
CyrusThePersian