This is not cognitive dissonance. It's not even an illogical argument. It's simply a statement that the present beliefs are always the "truth" in the sense that God wants JWs to have those beliefs at that point in time.
The counter-argument is flip-flops. Why would Jehovah direct, or allow the Society to direct, Witnesses to believe A, then change it to B, then back to A? Especially if the flip-flop led to lives being lost. This is true of the organ transplant flip-flop.
The counter-counter-argument to this is probably to say that Jehovah knew something that we didn't know, and people had to be steered away from organ transplants during those years. But it places the JW on shaky ground because they won't be able to point to anything we know now about transplants that made them dangerous from 1967 to 1980.
Another counter-argument is to ask where in the Bible God allowed his servants to have wrong beliefs for a period of time until he corrected them.