No cars will ever get 'stolen' 'lost' or 'hacked'..
As mentioned it'll be in there, it's either been misplaced (as in you're not seeing it in your garage but it is there) or you've gifted it and either forgot or done it by accident.
Some cars, like the concept cars, can appear lost when using the search feature i.e. driverain. For instance, my R35 TMS concept doesn't appear under 4WD on the filter, but change the filter to "--" and it's filed under there.
Whenever you see "--" in your filter, there'll be a car there that would normally come under FWD, MR, RW or 4WD, but this won't apply to your NASCAR.