You are right, i dont made a rockwell test with the Blade. So I really coud not know, if they are harder than the others.

But I sanded and polished more then 15 Blades and neither was so hard to polished, like this. There was nearly no abrasive effect on the metall. I sanded the double of time, dry and wet with the sanding rolls for the dremel and the effect is minor to my other blades.

I have not an idea, why?