I haven't found anything to show that they have, except in the Reasoning book, they admit say this:
"Jehovah's Witnesses do not claim to be inspired prophets. They have made mistakes. Like the apostles of Jesus Christ, they have at times had some wrong expectations.-Luke 19:11; Acts 1:6.
The Scriptures provide time elements related to Christ's presence, and Jehovah's Witnesses have studied these with keen interest. (Luke 21:24; Dan. 4:10-17) Jesus also described a many-featured sign that would tie in with the fulfillment of time prophecies to identify the generation that would live to see the end of Satan's wicked system of things. (Luke 21:7-36) Jehovah's Witnesses have pointed to evidence in fulfillment of this sign. It is true that the Witnesses have made mistakes in their understanding of what would occur at the end of certain time periods, but they have not made the mistake of losing faith or ceasing to be watchful as to fulfillment of Jehovah's purposes. They have continued to keep to the fore in their thinking the counsel given by Jesus: "Keep on the watch, therefore, because you do not know on what day your Lord is coming."-Matt. 24:42.
Matters on which corrections of viewpoint have been needed have been relatively minor when compared with the vital Bible truths that they have discerned and publicized. Among these are the following: Jehovah is the only true God. Jesus Christ is not part of a Trinitarian godhead but is the only-begotten Son of God. Redemption from sin is possible only through faith in Christ's ransom sacrifice. The holy spirit is not a person but is Jehovah's active force, and its fruitage must be evident in the lives of true worshipers. The human soul is not immortal, as the ancient pagans claimed; it dies, and the hope for future life is in the resurrection. God's permission of wickedness has been because of the issue of universal sovereignty. God's Kingdom is the only hope for mankind. Since 1914 we have been living in the last days of the global wicked system of things. Only 144,000 faithful Christians will be kings and priests with Christ in heaven, whereas the rest of obedient mankind will receive eternal life on a paradise earth."