It would make sense to take the cars from Flint County and add them to the same spots in the SF map, which leads me to a thought that I've had for a while-- why can't all the maps draw from a master vehicle list that covers the entire game world?
Just have a list that covers everything, then only spawn the vehicles that are within the boundaries for each map. For maps like NSA, spawn all the vehicles within its boundaries (from WV and LV) and add a few more (like Hydras) for specifically that map. This would make it really easy to make new maps, since it would only really require creating new boundaries and adding in additional map-specific vehicles if desired, assuming the new map covers areas that are in other maps.