I don't know Rich, but when I bought my car 50 years ago the guarantee plate still had traces of chrome where the attachment screws had protected it, likewise the oiler plates where the nipples &, on the right, the fuel pipes had protected them. I decided it had to be original so had them re plated.
Actually, they were all flash nickel plated. But the plating was so thin, much of it wore off after being polished a few times. Nowadays, all the repro plates you see are only unplated brass.
Ah! That explains. I'd always wondered why you'd polish chrome but nickel of course you have to. Oh well, it's a bit late I think to have mine stripped and re plated. Hey ho!