Few human beings ever have verbalizable access to all their evidence,

This being the case it indicates that the authority is screened of imperfectly, to the degree that the arguments are presented. For example if the arguments presented by the authority are flawed the degree of trust in their authority is drastically reduced. After all part of the information represented by the awareness of their authority is the expectation that their thinking wouldn't be terrible when they tried to express it. That turned out to be false so the earlier assumption must be discarded.