I have a 1971 CB500 I'm working on, build date 5/71.
I just rebuilt the caliper and master cylinder. Someone on Facebook asked about their master cylinder cap. It is concave and has no writing on it, just like mine. A few others chimed in with the same cap, and some people are saying it should have the decal.
The parts fiche isn't clear. However....the fiche shows the splash guard for the rotor, which mine doesn't have. When I Google 1971 CB500 images, none of them have the splash guard.
I believe my bike to be pretty original. Just out of curiosity, did the early 500's come with the plain, concave cap and no splash guard?