Yes, of course they work from a base map, anyone who thinks they start from a blank file would be a bit daft!
The point I'm making is that its a map specifically for your car, not just a generic one.
Obviously not as important on a standard car, but still, we all know all cars are not the same!
A garage I used to use a lot with my Cosworth and Cavalier Turbo do maps, I will pop over and see which he uses. I would also be able to get a before and after on the rollers too.