Now that I've stopped my cooking lessons via IM, and am able to go dig out my old NWT, here is more what I wanted to say before:
Since the Governing body teaches they're speaking for Jehovah:
Similarly today, a Governing Body composed of spirit-anointed Christians contributes to the unity of the worldwide congregation. The Governing Body publishes spiritually encouraging literature in many languages. This spiritual food is based on God?s Word. Thus, what is taught is not from men but from Jehovah. --Watchtower September 2010.
All who want to understand the Bible should appreciate that the ?greatly diversified wisdom of God? can become known only through Jehovah?s channel of communication, the faithful and discreet slave. Watchtower, Oct. 1 1994
And the New World Testament (their Bible) says in Deuteronomy 18:20-22 says:
"However, the prophet who presumes to speak in my name a word that I have not commanded him to speak or who speaks in the name of other gods, that prophet must die. 21 And in case you should say in your heart: "How shall we know the word that Jehovah has not spoken?" 22 when the prophet speaks in the name of Jehovah and the word does not occur or come true, that is the word that Jehovah did not speak. With preumptuousness the prophet spoke it. You must not get frightened at him."
The fact that they have made errors is very crucial, not something to not think about, because Deuteronomy shows that there will be many false prophets that claim to speak for Jehovah, and they will be known by their prophecies that don't come true, so by the Bible's own reasoning people who prophecy in the name of Jehovah and their prophecies don't come true are false prophets.