Larry,
I see your point when looking at
http://http://www.wwii-photos-maps.c...071216_011.htm
However, some photos show just the ZNr starting with the type code while other photos have the SU prefix.
Additionally, if you look at this target photo
http://www.wwii-photos-maps.com/targ...Amara%201.html for the airfield at Amara (Tunisia) it is coded FA 10 490.
Similarly, Sirte in Libya (
here is coded IA 10 93 on that document.