Amazon NX384PA

Amazon is one step closer to delivering its parcels by drones. The FAA gave its experimental airworthiness certificate to a testvehicle called MK021A on March 19th and registered it as 384PA. We presume it has the NX prefix although getting photographic proof would be highly unlikely. Its c/n is 000019, so where are the other 18? A further nine drones have been planned: N386PA/N388PA, N390PA/N392PA,N394PA,N395PA and N398PA.