Robert...(edit for correction)
Even stain resistant steels above the standard 13% chromium can corrode/oxidize given the right conditions. The only exception reported here is H-1. My suspicion is that the collective "we here" will not live long enough to see it, but the next generation will have someone who notices a rust spot on their H-1 Spyderco if the right conditions prevail. No, the knife world will not end because of it. But it will generate a lot of discussion about what we here didn't know now. LOL
Your conditions of cleanliness and care are within acceptable oxidation prevention practices. In this case it's not what you have or have not done. There may be a point on, likely below, the blade surface where an opening exists, not visible to the naked eye, that allows conditions to create a rust spot that you cannot reach with your preventative measures. It's taken 23 years for that to become evident.
It may be time for an above average penetrating oil to enter your ritual cleaning. I'd recommend G96 as I've seen it stop rust in its tracks. Before application of any oil you choose, warm the blade to evaporate any water that might be lurking at below surface levels. Even 100C/212F is not going to come close to affecting the heat treatment of the blade. But be careful. Put a drop of your chosen anti rust oil on the offending spots while the blade cools to help it penetrate. Then return to your 23 year successful maintenance program.
Last edited by Mike Blue
on Sun Mar 08, 2020 12:18 pm, edited 1 time in total.