I guess if we could hit a baseball-sized spot with 100% reliability (bear distances) we would see fewer of them go unrecovered. I'm personally not completely convinced this bear died from that shot. I would have bet MONEY it did, had I been there and seen the hit. But again, there is a certain degree of roulette when you combine internal anatomy, blade alignment/path, subtle animal movements or reactions, etc. Would the exact same hit produce the exact same outcome (unrecovered bear) most of the time? My thought is no...it wouldn't. Did the bear ultimately die? I think it's reasonable to believe it did but not until making it's escape good.
Would a 3-blade do better? Some say it would, but I'm not convinced. I too have had multiple instances of 3-blade heads skipping off ribs on angled shots and sliding between the chest and shoulder. I recovered one and proved it. Would a hit 4" forward produce 100% kill rates? I doubt it. Sooner or later Murphy shows up and wrecks our logic. Being logical humans we always try to find the logical answer to a puzzle, but in some cases the outcome is a matter of randomness and illogic. I can accept that, even if I don't enjoy having it happen to me.
Great discussion.