You learn something new every day.
My '73 had chrome clip ons. After I lost my first chrome one, I bought a pair of black clip ons used that I thought looked better anyway. Then another extra pair a few years later, as I decided that these are effectively a disposable part. The big problem for me (and maybe it's just my wiper motor spindle ?) is that the pattern of the grooves on the arm don't match the spindle, so how they even work at all I don't know, let alone stay on. Are mine mismatched I wonder ? A mechanic a few years back put "loctite" on them, and they stayed in place until restoration time, but now they'll have to go back on.
I've been trying to work out a more sophisticated solution to stop them falling off, if anyone has one I'd love to hear it. I had no idea there was a later design, I'd be really interested to see if anyone has pictures.
But to throw in my opinion/experience - the two pairs I bought used appeared to be original. If they had been originally chrome and painted black, it would be pretty obvious, I prepped and painted one set myself as they were a little rough, and the second set I had them done professionally. I have seen sets on ebay where they had just been painted black over chrome, so I know it happens. And the time I bought these parts, E9 values were not high enough, and parts were plentiful enough, that for someone to have gone to the trouble of stripping the chrome off and having them painted properly is hard to imagine. And in both unrelated cases.
Perhaps black wiper arms came with CSLs ? (Black slats in kidney grille, black headliner), someone will know.
Damien