That makes sense because prototype is not a status per se Perhaps we should add never entered service as well to cover where planes prototypes were built but never entered service and unbuilt or 0 to number of aircraft as well as never to first flight rather than leave them blank eg Aircraft first flight from to number status what it means Alpha A never 0 cancelled paper project Beta B never 2 cancelled prototype built but not flown Delta D 1978 1 cancelled prototpye built and flown Would this add to clarity