I thought I could pick a player separately for each series and assign them a car, but in setting up my 2012 cars, the Players seem to be crossing over between series, and then when I try to assign them a car, the cars from other series are … Very weird. Do you mean cup cars are showing up in the nationwide mod and things of that nature? Yeah, that is just odd. I would do what Wolf said, and be sure that all your cars in the proper folders. Also, if you download new 2012 cars, you should … …

Excerpt from:
Problem with Player Files – Sim Racing Design