The key really is to see if you can obtain a clean edge with no gaps or chip type spaces. Judging by the pictures, there is a lot of old rust and pitting in that blade. If you do circles with the 220 stone and check after a few sets of 40 circles (no more than 30-60 minutes) and are still not seeing a clean edge with more pitting going into the edge, I would say, time to find another blade.