Well that's true but I wouldn't call it a mistake. The then current and intended cartridge was the 455 Mk II and Smith's revolvers marked only 455 (when marked).

But it's also true that every 455 Mk II HE Smith produced was chambered long enough for the 455 Mk I at the behest of the Brits.

It's not unlike all 357s will also chamber 38 Specials but they're all referred to as and marked 357.

Other examples are 44 Mag/44 Spl, 32 S&W Long/32 S&W, etc.; they're all referred to and marked by their primary intended cartridge.

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Jim
S&WCA #819