Preservation class award is pretty low standard to get. Car cannot be "restored", but most anything can be maintained over the years using correct parts. new seat covers, partial resprays, are allowed. I think the line is crossed if you do a full respray and new interior + replate parts in engine bay.
you only have to pass 3 out of 5 categories.
If your car looks showroom, and isnt a true survivor then it's restored.