I "think" we are talking about ?3? mirror types: 1) early orig.mfgr double logo w/ pat.#'s, 2) later mfgr double logo w/o patent numbers and 3) most recent mfgr single logo.
I just looked at my mirrors, both the early patent number (original, first) manufacture type and the later manufacture no patent number type.
Type 1. Early orig.mfgr mirrors have two logos, "MS" and "Honda." These early.mfgr mirrors have other stamping around the the "MS" logo; i.e., "pat. 536563."
Type 2. Later mfgr mirrors have"HM" logo and "MS" logo with no patent number. The "MS" logo is smaller on the later mirror than on the earlier mirror. I can't say with certainty these later mfgr mirrors came from the factory on any sandcast or "K0" bikes or if they were replacement parts to original double logo mirrors. My personal opinion, i believe only double logo mirrors came from the factory on sandcast and "K0" bikes. If if mirrors with patent numbers and without patent numbers came on sandcasts is another question. (as an aside, i do know for a fact, double logo w/ pat.#'s mirrors came on K1 bikes and of course we know this mirror type did not use an acorn fixing nut.)
Type 3. "Most recent" (beyond early and later) manufacture Honda mirrors, until at least recently available from Honda, which come in Honda labelled parts boxes have no "HM" logo; only "MS" logo.
I've not seen mirrors from Yamiya, but i am assuming they are Honda "most recent" manufacture type.
Chris notes the pat.# is 536635. My mirrors have 536365 stamped on them. Assuming we have 2 different series of patent numbers, could this mean there are 2 different patent number mirror types ?