I don't think you can really count guys with great recovery powers or big hearts etc as would be the case with JMM and Calzaghe. Sure they have/had very good chins, but more so elite boxing skills which make it very hard to land(or follow up with) the type of shots that truly finish guys off, at least with any consistensy. Mayorga absolutely had one of the best chins of our era for the lower weights, the problem is that he relied on it and it got dented. If Calzaghe or Marquez fought like Mayorga did for a while no doubt they would have easily been knocked out, as is the case with the vast majority of fighters of any calibre. Watch him fight Vernon Forrest again, or Trinidad(both VERY capable of knocking guys cold). I can't really think of any other fighter who could actually use their chin as a weapon like that with any success. Mosley is about as freakishly tough as they come as well. Only Forrest ever actually hurt him and I suspect the headbutt is what actually did it for the most part. I can't really argue with the list other than adding Mayorga I guess.