Steve,
I think you will find that the rubber surround to the mirror was fitted in the late 60's to these mirrors. I believe it was aimed at meeting new safety standards, re sharp objects to hit heads on. The black plastic toggle to the dipping switch, replaced the earlier white ball.
The NOS original mirror i have doesn't have the rubber surround or the black toggle.
All the original cars i have seen , have not had the rubber surround fitted to the mirror.
Hope that helps.