I'm well aware that 303 cannot be HT'd. However, as in informal poll. how many makers HT their 416 bolsters? IMHO, very few. None that I know personally. The 400 series are HT'dx to increase corrosion resistance. It's not a problem with 300 series. We're talking hardware, not blades. Wrought iron and 1018 really can't be HT'd, nor can brass, NiSil nor bronze. They are ornamental.
I have no problem at all with 303 for hardware. If I'n using a bar end of ATS or 154, I may HT it for hardware, just to increase corrosion resistance. It depends on where the knife is going and the intended use.
Gene