The quotations on this page clearly show how the Watchtower has changed its own history by re-writing its own literature in an attempt to avoid being revealed as a false prophet.
"That the deliverance of the saints must take place some time before 1914 is manifest...Just how long before 1914 the last living members of the body of Christ will be glorified, we are not directly informed;" (Studies in the Scriptures, Vol. 3, p. 228).
Rewritten
"That the deliverance of the saints must take place very soon after 1914 is manifest... Just how long after 1914 the last living members of the body of Christ will be glorified, we are not directly informed;" (Ibid., 1923 ed.)
"This calculation shows A.D. 1874 as marking the beginning of the period of trouble; for 1542 years B.C. plus 1874 years A.D. equals 3416 years. Thus the Pyramid witnesses that the close of 1874 was the chronological beginning of the time of trouble..." (Studies in the Scriptures, Vol. 3, p. 342, 1889 ed.)
Rewritten
"This calculation shows A.D. 1915 as marking the beginning of the period of trouble; for 1542 years B.C. plus 1915 years A.D. equals 3457 years. Thus the Pyramid witnesses that the close of 1914 will be the beginning of the time of trouble..." (Ibid., 1905 ed.)
"Also, in the year 1918, when God destroys the churches wholesale and the church members by millions..." (The Finished Mystery, 1917 ed.).
Rewritten
"Also, in the year 1918, when God begins to destroys the churches and the church members by millions..." (Ibid., 1926 ed.)
These are some of the writings foundational to Watchtower history, but what of more recent examples?:
"Also, as reported back in 1960, a former United States Secretary of State, Dean Acheson, declared that our time is "a period of unequaled instability, unequaled violence." And he warned: "I know enough of what is going on to assure you that, in fifteen years from today, this world is going to be too dangerous to live in." (The Truth that Leads to Eternal Life, p.9. [as published prior to 1975]).
Rewritten
"Also, as reported back in 1960, a former United States Secretary of State, Dean Acheson, declared that our time is "a period of unequaled instability, unequaled violence." Based on what he knew was then going on in the world, it was his conclusion that soon "this world is going to be too dangerous to live in." (The Truth that Leads to Eternal Life, p.9. [as published after to 1975]).
Note that this was changed after the significant Watchtower date of 1975, which was strongly hinted to be the date for the beginning of the millennium reign of Christ, failed to materialised.
"The apostle Paul was spearheading the Christian missionary activity. He was also laying a foundation for a work that would be completed in our 20th century." (w89 1/1 12 "The Hand of Jehovah Was With Them" [as originally published in the Watchtower magazine]).
Rewritten
"The apostle Paul was spearheading the Christian missionary activity. He was also laying a foundation for a work that would be completed in our day." (w89 1/1 12 "The Hand of Jehovah Was With Them" [as it appears in Watchtower bound volumes & CD-ROMs])