Another difference between the Original Gamemaster and the Newer "Classic" was that Jack molded a metal rod into the riser. This was to increase rigidity. The black section on the Gamemaster and the Classic risers is Jacks own formula of plastic. He actually mixed and poured the formula himself. On a "Classic" you can put a magnet to the riser and it will hold on. Jack claimed that handle rigidity was a key factor in his increased speed.
As Kelly stated, Jack never even shot his Classic model. By the time he introduced it, he was into his '80's.
While Jack's philosophy was "there is only one right way to make a bow", He did do a bit of variations whne he came out with the Classic in that he also introduced the "Carbon Cassic" with carbon limbs instead of his standard Glass. At that time, no more Jets were supposed to be made, but he did make a few on special order only. A very few he made with carbon also.