It took the WTS until 1943 to totally dump 1874, from 1879 to 1943 would be 64 years.
“THE SCRIPTURES SHOW” JESUS RETURNED IN 1874
From 1876 Charles T Russell (who founded the Watchtower Society-the publishing/legal channel of the Jehovah’s Witness sect) promoted 1874 as the date for Christ’s return and the start of Christ’s “invisible presence”.
That Christ returned in 1874 was official doctrine until 1930. Note:
...the Bridegroom came in the Autumn of 1874, and he appeared to the eyes of faith-seen by the light of the lamp-the Word.
(Zion’s Watch Tower Reprints October/November 1881 p. 289)
Our Lord’s presence as Bridegroom and Reaper was recognized during the first three and a half years, from A.D. 1874 to A.D. 1878. Since that time it has been emphatically manifest that the time had come in A.D. 1878 when kingly judgment should begin at the house of God.
(Studies in the Scriptures Vol. II 1889 p. 239)
…he [Jesus] would in reality assume the kingly office, power, etc.; viz., in the spring of 1878, three and a half years after his second advent at the beginning of the harvest period, in the fall of 1874.
(Studies in the Scriptures Volume III 1891 p. 234)
Our Lord, the appointed King, is now present since October 1874, A.D., according to the testimony of the prophets, to those who have ears to hear it: and the formal inauguration of his kingly office dates from April 1878, A.D.
(Studies in Scriptures Vol. IV 1897 p. 621)
Pastor Russell...believed and taught that we are living in the time of the second presence of our Lord, and that his presence dates from 1874...
(WT December 1, 1916 p. 5998)
Fall 1874 A.D. Second Advent of the Lord
(The Finished Mystery 1917 p. 60)
Some of the Scriptures, which, when understood in their connections and significance, prove that the Lord’s Second Advent occurred in the Fall of 1874 are as follows:
[A list of 88 interpretations followed]
…and these are but 88 of the proofs hastily collected.
(The Finished Mystery 1917 pp. 68, 71)
The time of the Lord’s second presence dates from 1874...
(The Harp of God 1921 p. 231)
The Scriptures show that the second presence (of the Lord) was due in 1874... This proof shows that the Lord has been present since 1874...
(WT March 1, 1923 p. 67)
Surely there is not the slightest room for doubt that in the mind of a truly consecrated child of God that the Lord Jesus Christ is present and has been since 1874.
(WT January 1, 1924 p. 5)
The second coming of the Lord therefore began in 1874...
(Creation 1927 pp. 289, 291, 297, 298, 318)
The Scriptural proof is that the second presence of the Lord Jesus Christ began in 1874 A.D.
(Prophecy 1929 p. 65)
From 1874 onward is the time of the Lord’s second presence, as above stated…
This circumstantial evidence fulfilling prophecy is what constitutes the physical facts, and is proof corroborative of the Lord’s presence since 1874…
His presence beginning in 1874, he has carried on his harvest work from 1874 forward…
(Our Lord’s Return 1929 pp. 27, 33, 37)
JESUS’ “RETURN” SWITCHED FROM 1874 TO 1914
In 1930 Christ’s return and “presence” was switched from 1874 to 1914.
In The Golden Age magazine (1930 p.503) Joseph Rutherford, the second president of the WTS, wrote “Jesus has been present since 1914” but he gave no supporting explanation. In 1932:
The prophecy of the Bible, fully supported by the physical facts in fulfillment thereof, shows that the second coming of Christ dates from the fall of the year 1914.
(What is Truth? 1932)
Until 1943 there was little further mention of this doctrinal change. Then in 1943 the WTS published The Truth Shall Make You Free which revised the WTS’s Bible chronology by bringing the date of Adam’s creation 100 years forward. This removed any remaining prophetic significance of 1874. Christ’s return in 1914 thus became the official truth for Jehovah’s Witnesses (JWs).
After switching Jesus’ “return” from 1874 to 1914 the WTS writers began to claim or imply that their early Bible Students had anticipated 1914 as the date of Christ’s “presence” from their beginnings!
Consider some examples:
DECEITFUL CLAIM REGULARLY REPEATED
As for the time of Christ’s second presence, Daniel’s prophecy is again the one that gives the chronology for it. (Dan. 4:16) It was figured out as pointing to A.D. 1914, and The Watchtower called notice to the significance of 1914 in the year 1879.
(WT 1952 November 1, p. 658)
Why, then, do the nations not realize and accept the approach of this climax of judgment? It is because they have not heeded the world wide advertising of Christ’s return and his second Presence. Since long before World War I Jehovah’s witnesses pointed to 1914 as the time for this great event to occur.
(WT 1954 June 15 p. 370)
Bible chronology also fixes the time for Christ’s second presence and the assuming of his right to rule as at 1914; this date was published in the Watchtower as early as 1879, 35 years before 1914.
(Tract: Sign of Christ’s Presence 1955 p. 3)
…history confirms that Jehovah’s witnesses were the only Christian group found awake as to 1914…
(WT 1960 July 15 p. 433)
As we look back over the years, we can clearly see how God’s organization in modern times has progressed in understanding. For example, it learned that Christ’s second presence was to be in the spirit, and not in the flesh as many professed Christians believe. His rule would be from the heavens. This was a new revelation of great importance to God’s people who had been anxiously awaiting his second presence toward the end of the nineteenth century.
(WT 1965 July 15 p. 428)
For over thirty years before that date and for half a century since, Jehovah’s witnesses have pointed to the year 1914 as the time for the end of “the appointed times of the nations” and the time in which Christ would begin his Kingdom rule. (Luke 21:24)
(WT 1966 February 15 p. 103)
“Do you believe in the second advent of the Lord?” I asked the young man [a WTS colporteur in 1928] who came to the door.
“Christ’s second advent was realized in 1914” he answered.
In astonishment, I told him that was impossible. “You should read this book,” he said, handing me The Harp of God. I was baptized the following year, March 23, 1929...
(WT 1988 May 1 p. 22)
[Note: Nowhere in The Harp of God (1921) is the “second advent” of Christ put in 1914. On the contrary, 1874 as the date of the “presence” of Jesus is mentioned in The Harp of God on pages 230, 231, 234, 235, 236, 237 241, 244, 271). Also “the young man” could not have known in 1928 that “Christ’s second advent” was realized in 1914” because that teaching had not been published at that time! Even the later editions of The Harp of God (1937 & 1940) retained 1874 as the date of Christ’s “presence”.]
He [a WTS colporteur of 1921] explained to me that Jesus had been present since 1914, invisible to man. This was the most thrilling news I had ever heard... In late 1921 I was transferred back to England, and in the spring of 1922, I was discharged from the army.
(WT l990 September 1 p. 11)
[Note: When this purported conversation occurred in 1921 no WTS publication had mentioned 1914 as the date for the “return of Christ’’-nor for nine years afterwards!]
The Watchtower has consistently presented evidence…that Jesus’ presence in heavenly Kingdom power began in 1914. Events since that year testify to Jesus’ presence.
(WT 1993 January 15, p. 5)
…a prophecy providentially caused sincere 19th-century Bible students to be in expectation. By linking the “seven times” of Daniel 4:25 with “the times of the Gentiles”, they anticipated that Christ would receive Kingdom power in 1914.
(WT 1998 September 15 p. 15)
This thread as some more info.
http://www.jehovahs-witness.net/watchtower/beliefs/99372/1/Even-seen-or-read-this-booklet-anything-about-Christs-return-in-1914-1874