Gary at Tiny Wheels, had brought up this point a short time ago regarding the Street Freaks series. As I recall he had mentioned that in one or two releases he had found the same vehicle with or without the game piece and some inner boxes completely with or without the game pieces while others were mixed.
Maybe you can find this thread or Gary will be kind enough to discuss it in detail again.
I think JL was planning on ending this promotion/contest in November. I was under the assumption that they were slowly withiirng out of the program by randomly placing gamepieces on JL cards until all the gamepieces were released. Thats MHO!