Watchtower May 1,1997 pg. 8:
Jehovah God is the Grand Identifier of his true messengers. He identifies them by making the messages he delivers through them come true. Jehovah is also the Great Exposer of false messengers. How does he expose them? He frustrates their signs and predictions. In this way he shows that they are self–appointed prognosticators, whose messages really spring from their own false reasoning–yes, they are foolish, fleshly thinking.
So Rutherford, acting as FDS, was one of them. He made an ass of himself as he said.