My experience is this:

In 1997 I took my chain plates out and had them die penetrant tested. I thought the looked good but the stainless guy said "see that line". I could barely see it. He proceeded to bend the 3/8" SS at the hairline with his bare hands. The crevice corrosion was 90% of the way through. I said replace them all - the other chainplates had similar, but not as extensive hairlines with the dye.

Flash forward to 2008. Same location (New Zealand) - same stainless guy. Had them electropolished and they tested good.

The only difference was that the ones done in 1997 were 316.

The boat was built in 1985.