::::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?