There is no doubt that the Watchtower was a bit confused as to whether or not 1975 would be the end. Nevertheless, they said what they said:
*** Awake! October 8 1968 pp. 14-15 ***
6,000 Years Nearing Completion […] The fact that fifty-four years of the period called the ‘last days’ have already gone by is highly significant. It means that only a few years, at most, remain before the corrupt system of things dominating the earth is destroyed by God. Today, many years later, we may ask, What does the phrase ‘the immediate future’ mean? How many years are ‘a few years at most’?…only seven more years from the autumn of 1968 to complete 6,000 full years of human history. That seven-year period will evidently finish in the autumn of the year 1975
But here they seem not so certain:
*** Watchtower 1968 May 1 pp.271-3 Making Wise Use of the Remaining Time ***
THE SEVENTH DAY
7 The immediate future is certain to be filled with climactic events, for this old system is nearing its complete end. Within a few years at most the final parts of Bible prophecy relative to these “last days” will undergo fulfillment, resulting in the liberation of surviving mankind into Christ’s glorious 1,000-year reign. What difficult days, but, at the same time, what grand days are just ahead!
8 Does this mean that the year 1975 will bring the battle of Armageddon? No one can say with certainty what any particular year will bring. Jesus said: “Concerning that day or the hour nobody knows.” (Mark 13:32) Sufficient is it for God’s servants to know for a certainty that, for this system under Satan, time is running out rapidly. How foolish a person would be not to be awake and alert to the limited time remaining, to the earthshaking events soon to take place, and to the need to work out one’s salvation!