All the Q?+?? codes mentioned by Peter can be found as part of the LEMB Sktz Database Project, a direct to link to which can be found below:
http://www.luftwaffe-experten.org/stam-q.html
As for a He219A-7 coded QT+NY, there is nothing listed that is anywhere near this in the "Other Known Werknummern or Signs" of "Heinkel He219, An Illustrated History" by Roland Remp [Schiffer, 2000]. The image in "Luftwaffe Combat Aircraft of Hitlers luftwaffe 1939-1945" appears to be a heavily retouched wartime photo...
Kind regards,
Peter D Evans
LEMB Administrator