The tool maker where I worked in the 70's used to distinguish what he called "true" stainless from the other alloys. He said true stainless was one particular alloy, used mainly in surgical instruments and implants, but which was not tough enough for many applications, guns and hunting knives, included. It was an austenitic stainless in the 300 series, IIRC. Today there are both austenitic and martensitic stainless alloys for medical applications. I guarantee they don't want someone with a knee replacement either rusting out or attracting the magnet in the MRI machine.
The stainless Buck hunting knife sitting on my workshop table attracts a magnet and will rust a little, but it does neither as well as conventional carbon steel. It's the comparison you want to look for. The cold blue test is a good one. They do make cold blue for stainless, but it really doesn't work as fast as cold blues for regular steel, nor is the result as dark, being more like a charcoal gray.