Thank you Simon, that's interesting info.The mention of the white / blue with red lettering came from wikipedia and is related to NW Europe 1944-5 so possibly a red herring. I think you may be on the right track when you say about the bar being added later. It could of course be 'repainting' of the bar? I wonder also how much the lighter colours changed due to 1. Dust / dirt and 2. Fading due to the intense sunlight (I have other photos from this set which show vehicle tyres being kept covered due to the heat ). Looking for example at the bridging plates the number 5 looks very faded - one could believe it wasn't black but I can find no mention anywhere of them ever (during this period) being other than 'Black on Golden Yellow'If you look at the photo that's not an MW (not sure what it is) it looks as though the bottom bar is not white but white/blue? I thought this was the effect of a shadow but another photo suggests otherwise - agin though, not something mentioned elsewhere.
Where did you find the info on the 465/468 46o series AoS numbers please?