Perhaps the Rotordyne design could have prevented the development of the Osprey had it gone into Production.
Maybe cheaper too?
I've found this stamp from Kampuchea which seems to show an image of the Rotordyne but it has also created a number of questions such as did Kampuchea ever buy a Rotordyne? The date 1987 is also a bit strange because Kampuchea was supposed to be Cambodia by then?
Apparently if you were in Kampuchea in 1987 your letter may have had one of these Rotordyne stamps stuck on it.