I don't know what kind of stainless they used back then. I had three different folders smack in the middle of the 70s as I was looking for something that wouldn't rust so easily whilst carrying out my duties as a laborer/pack mule on a construction job.
The knives were typical CASE construction then. Gorgeous mahogany bone, great snap/fit/finish. Pretty just to look at.
They had most miserable, awful steel I have ever had on any pocket knife I have ever owned to this day. Exposure to air made that steel dull. It was awful to the point of unusable. It was soft, ground differently than their regular carbon, and never felt right on the stone when sharpening. I traded the last one I had away (the first two were gifts on the same Christmas) and got myself a 4" CASE copperhead in '76, which worked like real knife and I actually have that exact knife today. Still has another 100,000 miles left on it even though the jigging is pretty smooth, the heads on some of the pins are gone, and the snap is noticeably weaker than when new after about 10 years of constant carry. Still like to carry that one.
Fast forward to a couple of years ago, and I tried out a CASE medium jack (pattern # unknown) in stainless. It performed almost exactly as the CASE knives I have in carbon. Steel is a bit soft as CASE seems to be to me, but it allows one to get a screaming edge with little effort. I don't know when they started getting their stainless right, but if the rest of their stainless is like the newer model I tried out, it would be a good knife to have.
Robert