kenello I believe that the Jetstream 3x had a UK limit and an international limit due to some difference in the weight of a test bird. As you say the windows where tested with one weight of bird which was accepted by everyone bar the CAA and to keep them happy when the difference was discovered they dropped the Vmo by 10 knts to get a CAA signoff.
The swedish/danish Jetstreams which are operating in the UK have different barber pole settings to the UK reg ones.