I thiink WT leaders trust their own thoughts as the ultimate authority as well. They have convinced themselves that they are the "faithful and discreet slave," so whatever their minds come up with is "truth" given them by holy spirit. What they teach is "the truth" until they change it by getting "new light" (meaning until their minds come up with something different).
Their fanciful Bible typologies have led to all manner of false teachings and failed predictions.
Russell came up with chronological charts that had symmetry, so they HAD to be correct... He convinced himself that the Great Pyramid was "God's stone witness" so its measurements supported his charts (he even changed the length of the great passageway from one edition of his book to the next to accommodate a 40 year adjustment in his date system). He convinced himself that 1914 would be the date for Armageddon. When that turned out to be wrong, instead of abandoning the date as wrong, Rutherford changed it into the year of Jesus' "invisible presence" (which Russell taught was 1874).
Rutherford came up with the date 1925 for the resurrection so in Millions Now Living Will Never Die, the Bible's Jubilee cycles "proved" 1925. After 1925 came to nothing, instead of saying, "I was wrong" (like Harold Camping finally did), Rutherford just kept going and had the WTS build Beth Sarim for the patriarchs. He came up with the two-class system, so JWs believe the Bible teaches it. (Rutherford also had a "Ruth class", an "Esther class," a "Mordecai class," and on and on. These individual "classes" have been abandoned by later WT leaders, but for years they were "the truth" because Rutherford trusted that what made sense to him was truth/)
Livid that he had been sent to prison, Rutherford decided the "governing authorities" of Romans 13 couldn't be the world's governments, so he taught they were Jehovah and Jesus. Because of this, many JWs were forced to go to prison over the draft issue rather than being allowed to agree to alternative service.
Fred Franz became convinced in his own mind that the "sabbath rest" of the "new system" had to parallel the six "thousand year days" of creation (another construct of WT leaders' minds). Based on his calculations, he hyped 1975 as "an appropriate time for God to act." He published as truth what his mind had produced and persuaded many JWs to give up homes and jobs to pioneer so as to promote his chronology of the end. It was the truth because he was the primary theologian of "God's organization". What he wanted to be true WAS true...
Today there are millions of JWs worldwide whose lives are totally dependent on what a small group of JW leaders convince themselves is true. The fact that they think it is true is sufficient for them, because they have convinced themselves that they are God's channel of communication and that their thoughts come from God.