Found it on BladeForums:

"Schrade stainless was originally 440C, until in the late 1970s they trademarked Schrade Plus for 440A which had a special heat-treat, enabling the steel to come out of the heat-treat with two points more carbon than it went in. (i.e., originally, about .6 carbon, after heat-treat, .8 and a fine grain structure.)"

Good stuff!