I recently cashed in two of those heavily restricted RTW certs for a regional domestic flight (800 miles or less from origin to destination). We're flying ATL-IAD nonstop, and on the return we're flying BWI-ORD-ATL. The certs specified that they were only good for roundtrips (no circle trips or stopovers). Therefore, I think BWI/IAD/DCA are still considered coterminals for travel.