Actually the "we are only human" is usually a phrase from the followers, not the leaders. The closest thing to this is the Watchtower of 1980 that attempts to explain the 1975 predictions:
w80 3/15 p. 17 pars. 5-6 Choosing the Best Way of Life
In modern times such eagerness, commendable in itself, has led to attempts at setting dates for the desired liberation from the suffering and troubles that are the lot of persons throughout the earth. With the appearance of the book Life Everlasting—in Freedom of the Sons of God, and its comments as to how appropriate it would be for the millennial reign of Christ to parallel the seventh millennium of man’s existence, considerable expectation was aroused regarding the year 1975. There were statements made then, and thereafter, stressing that this was only a possibility. Unfortunately, however, along with such cautionary information, there were other statements published that implied that such realization of hopes by that year was more of a probability than a mere possibility. It is to be regretted that these latter statements apparently overshadowed the cautionary ones and contributed to a buildup of the expectation already initiated.
6 In its issue of July 15, 1976, The Watchtower, commenting on the inadvisability of setting our sights on a certain date, stated: "If anyone has been disappointed through not following this line of thought, he should now concentrate on adjusting his viewpoint, seeing that it was not the word of God that failed or deceived him and brought disappointment, but that his own understanding was based on wrong premises." In saying "anyone," The Watchtower included all disappointed ones of Jehovah’s Witnesses, hence including persons having to do with the publication of the information that contributed to the buildup of hopes centered on that date.
So the Governing Body never admits it is wrong, but lets the followers cover for them by using the "human" card. But is this actually encouraged? NO. Published just last year:
w05 9/15 p. 20 par. 18 Walk by Faith, Not by Sight! ***
As Jehovah’s modern-day servants, we cherish our good relationship with God. We are eager to learn and apply in our lives valuable lessons from past events. (Romans 15:4) When the Israelites walked by sight, they forgot that God through Moses was directing them. If we are not careful, we too can forget that Jehovah God and the Greater Moses, Jesus Christ, are directing the Christian congregation today. (Revelation 1:12-16) We must be on guard against taking a human view of the earthly part of Jehovah’s organization. Our doing so can lead to a complaining spirit and a loss of appreciation for Jehovah’s representatives as well as for the spiritual food provided by "the faithful and discreet slave."—Matthew 24:45.