What interested me about that stone was the 44 soft label didn't have the usual border escher put around their end labels. I have seen a few with "Guaranteed Soft" on one end and Gelb-Gruhn or Yellow Green on the other end. Both labels having the border , IIRC with E&Co in the center at the bottom in small print. I think it means that a soft hone is preferable to some, perhaps because it cuts faster ? Here is an old post with examples of end labels that I'm talking about.