A question about rear mudguards...

[westlake17]

I have noticed that many heavyweight models from the fifties have the same type of rear mudguards. I have seen some small changes in how the rear portion of the mudguard is attached to the front portion: Some have a hinge, some have one or two chromed bolts on top of the mudguard. My 1955, 18S has one chromed bolt on top (and one more on each side).
Does someone know when these changes took place?

/Mats

[Rob Harknett]

I have not checked all the parts lists, but can confirm 1955 had the single bolt for standard road models.
I believe sports models differed in some way. So the changes , if noted would be for certain models, not the whole range.