The post CPSC holders came with injection molded plastic coverings for the USA market as that was the way Campagnolo chose to attain the CPSC standard, it was a puncture standard, so there was not a "mandate" per se, just a test to pass.

Originally in chromed steel, later later Super Record had alloy holders with the black plastic, ABS by the way, I have done a burn test. Also, not all plastic covered holders had the Campagnolo typography underneath, some did some, did not. I have one Colbalto brake caliper with the blond plastic and O ring and chromed holders... Do not ask Italians for consistancy.

Some of the G.S. caliper holders were cad plated just to confuse things, with chromed nuts and washers...

The alloy holders used stainless steel hardware, the stud and washer and nut were all stainless.

The conical nuts I have seen OEM were chromed steel. Not that ALL are.

In a few instances I have been able to ebay win some holders, but also have purchased complete calipers for less than the price some holder auctions close at. There is no logic here, just timing.