According to WTS definition of "The Truth," they simply don't have the truth:
?The truth will not allow for all the different kinds of religious doctrine in the world?There can not be two sets of truth when one does not agree with the other. One or the other is true, but not both. Sincerely believing something and practicing that belief, will not make it right if it really wrong.?
--from: You can live forever in Paradise on Earth, page 32.
?If our worship is to be acceptable to God, it must be firmly rooted in God?s Word of truth. Jesus reproved those persons who claimed to serve God but who relied heavily on the tradit- ions of men in preference to God?s Word?
--from: The Truth that leads to Eternal Life, page13
"If we following a man undoubtedly it would be different with us; undoubtedly one human idea would contradict another and that which was light one or two or six years ago would be regarded as darkness now. But with God there is no variableness, neither shadow of turning, and so it is with truth; any knowledge or light coming from God must be like its author : A new view of truth never can contradict a fomer truth. 'New Light' never extinguishes older 'light,' but adds to it."
-- from Zion's Watchtower, Feb.1881, page 3