I would think Hornby has got the blanked windows correct for a proportion of the CCTs.   Quickest way to prove that would be to check out these links.   http://www.scienceandsociety.co.uk/results.asp?image=10443238&itemw=4&itemf=0003&itemstep=71&itemx=119   http://www.scienceandsociety.co.uk/results.asp?image=10443239&itemw=4&itemf=0003&itemstep=71&itemx=120   Maybe it was just done for CCT's used in car carrying traffic?   Porcy