And here's another small theory from the same man:

Learn about car prizes in Gran Turismo 2 special events. Discover how to win multiple different cars from the same race.

It appears that in Gran Turismo 2's Special Events, any of the three cars associated with a particular special event can be won from any of that event's races. You can win three different cars by repeatedly winning a specific Special Event race, and this has been confirmed with several favorite Special Event races. However, no more than three different cars have been won for the same race.