AFAIK, all FL and FD lenses with the silver breech lock collar are marked if they are S.C. or S.S.C., even though I believe that by the late 1970s, all FD lenses were one of the two. When the FDn lenses came out, multicoating was such a given that they stopped marking the lenses.

So, if it is a silver breech lock lens, it should be marked, but none of the FDn lenses are marked, even though they all have it.