I don't know if ONLY the original works... or if GVT simply only does its thing once.
I did the original program that came out in MM2K. I got great results on that one... so did my wife. It was kind of the rage at Gold's at the time... so everybody was trying it. It was a truly killer workout... and a huge number of people dropped out. They couldn't complete it.
It seemed like everybody who completed the program had good results... all about the same 7-8 lbs of muscle mass and much strength.
The original program had 2 additional phases. Many of us tried the additional phases... no one had good results even though many of us finished the programs. I later tried another variation... again with no good results.
So... who knows. I got great results... but only once. I've never met anyone who got good results doing GVT twice.
This could be because the "over training" element is heavy. You finish a couple months on GVT desperate to take a break. I don't think I would have stuck with it if the program were even 3-4 weeks longer. (Leg day... you would see guys dripping sweat onto the floor. No joke.)