The reason Derbyshire Wayfarers are only meant to be issued at nominated locations is entirely down to the sleeve (buses carry them, train crew do not). In practice we can issue them on board (IE mobile machines won't refuse to issue them like some tickets) but I generally warn passengers that they may get grief from bus drivers expecting to see the sleeve if indeed they want to use a bus at all. The sleeve is intended to be used to complete a log of journeys made on the ticket which you can then send in to the council to be entered into the draw for further free tickets.