It appears to me that a common characteristic of a cult is to affirm that the Bible is God's Word & true; yet upon closer examination it proves that it is the Bible only as interpreted by the cult leadership which is the actual authority. Thus if you are debating doctine with a JW on the porch, remember that the Witless you are arguing with probably believes that the Watchtower Leadership is itself a prophet, even it it has been proven false by failed predictions of Christ's Return.

Similarly when debating a RCC person, he may seem to be debating with you what scripture means, but he probably is committed to the false POV that scripture means only what the pope says it means.

Thus the final authority is not the Bible for such persons, but human tradition, which as in the case of the Pharisees, trumped the Bible.