Whether Bush was an eligible player or not for that game. Even if the NCAA agrees that there is nothing USC could have done to prevent Bush or his family from receiving extra benefits, or having an "arrangement" with an agent (remember, if a kid HIRES an agent, he can't play college football)--the FACT that they received benefits or even had a verbal agreement with an agent means Bush lost his amateur status. The only basis for appeal is WHEN that happened.
FWIW, Cal vacated games that Ainsworth and Davenport played in under Holmoe because they were declared to have been ineligible. Also, FWIW, I think the rules on agents are stupid. College kids should be able to hire an agent and test out the draft and if they don't want to go, should be able to return to college ball. Also, college kids should be able to get loans (from agents or just speculators) based on their future earning potential, just so it is tied to only that and not what college they choose to play for. Maybe say they cannot have contact with any agent until AFTER they have signed LOIs and the agents cannot have ties to the program they sign with.
It is nuts that, for example, John Elway made $100,000 (a lot of money in the early 80's) playing for the Yankees during each his last two summers while at Stanford and could still play college football as an "amateur athlete" but the NCAA technically could make a fuss about a booster giving a kid a hot dog at a tailgate.