Green's Last Book
I think William Green's last work was "Aircraft of the Third Reich 1933-45 Vol.1" published by Aerospace around 2010. It is a comprehensive and impressive book covering more than just warplanes of the Luftwaffe. I was looking forward to the planned volumes 2 and 3 but Aerospace Publishing ran into difficulties and they never materialised.
Much like his "Aircraft of the Second World War" series I suppose.