Yep, not enough data to waste too much time theorizing. But interesting, nonetheless. Maybe marginal stabilization and/or weird impact angle/bone angle, etc. I've had my share of good and disappointing experiences with that bullet type. And enough experience with inexplicable terminal results with almost any bullet that I won't question the story of a reliable guy. I still use them - just have a better understanding of the parameters for success. (I once killed a big doe with a hi-speed light 85 gr varmit frangible from a 25/06 that hit the shoulder and never penetrated the rib cage. Critter still died, but an awful mess.)