"I'm also curious on, for instance, Tesla's "200 mile range". Is that a true 200 miles, as in I can get to a charger at 195, or could I potentially go dead at 170, especially with older batteries? Also, 200 miles on flat ground? What about more aggressive driving, grades, etc?"
As with other mileage figures for gasoline and diesel, it's going to be affected significantly by driving style, driving conditions, and the like.