Regarding 1975 I was shocked to learn (from reading ex-JW books by Franz and Penton) that the 1975 date first began to be taught in 1966 (in the Life Everlasting - in Freedom of the Sons of God book). I had long assumed it began being taught much earlier, since it was based up when the 6th creative day supposedly started. But I remember that in the Proclaimer's book the WT said they added about 100 years to when the 6th creative day would end (teaching in Russell's time that it ended in 1874), to discovering a problem (they claim) with the KJV translation of a verse. Long before then Rutherford had moved the teaching pertaining to 1874 to 1914 (or he had dropped the 1874 date and after Rutherford died the WT began substituting the 1914 date for the 1874 date) - but my memory is fuzzy on the details about this.
Rather than the year 2034, the years 2030 and 2033 make more sense to me. That is because it is commonly taught that Jesus began his preaching in the year 30 AD (CE) and was crucified in 33 AD (CE), and if we converse the WT date of when Adam was created as a result of thinking of biblical years of a 360 day prophetic calendar (instead of an approximately 365.2524 day solar calendar), then we get the date of about 3968 BCE as the date of Adam's creation and that is about 4000 years before 33 CE! That means Christ would return about 6000 years after that year, namely in about 2033. [4026 x 360/365.2524 = 3968.105, hence 3968 BCE for Adam's creation date instead of 4024 BCE; 3968 BCE + 6000 solar years +1 solar year [due to no year 0] = 2033 CE).
It is interesting to me that the 2033 CE date is very close to the date which some calculated as 1914 CE plus 120 years (= 2034 CE).
Usher had calculated the creation of the world and of Adam as being 4000 years before the birth of Christ (which I think he believed was on December 25, 1 BC) and he thus got the year of 4000 BC as the creation date. Some people then added 2000 years to that and got 2000 AD/CE (or 2001 AD/CE0, but I (and ideas I read of someone on the internet) think it makes more sense to add 2000 years from the year Christ began his ministry or to the year Christ died - instead of to his year of birth.
The dates of 2030 and 2033 are ones I came up while I was an independent Christian (somewhere around the year 2007). Though I am now an atheist I sometimes hypothetically wonder that if I am wrong in thinking there is no heavenly Jesus Christ, will Christ appear in judgement in the year 2030 or 2033. Along those lines I wonder if the tribulation will begin in 2030 and if Christ will come in judgement 3.5 years later and if something supernatural might take place in 2036 (or 2037).
Keep on the watch for the years 2030 CE - 2036 CE.