I can only report of what I have seen and experienced myself, which is not a flawless record by far. The bullet is at times failing before it gets past the fat layer. If it strikes bone it easily penetrates just not wet tissue.
I remember specifically once shooting a possum at point blank range. At these ranges I hold the cross hair on the top edge of the body above the forward torso. this puts the projectile at about 1 and a half inches below my aiming point. I actually witnessed the impact and the blood but the animal ran off. After examining the mess I had to conclude bullet failure. There was fat, blood and fur splattered around.
There have been other instances, once with a raccoon where blood, fat and fur were at the location however that time the animal was a further distance and didn't witness a detailed impact.
I have shaken my head at hits on squirrels that should have been lethal. One squirrel in particular was covered in blood from the first hit but little penetration.
One of the crows I have killed with the 17hmr had a huge blown out cavity at the entrance of the impact but not very much penetration.
If the wound is superficial than it opens up the very real possiblity that the animal will not die any time shortly and may even survive the injury albeit the creature will be hideously maimed and scarred. A upper torso hit should result in death even if it doesn't happen right away, by penetration into the critical organs and blood vessels.
I find it rather hard to believe I would be the only one who has witnessed bullet failure from the 17hmr. A hunting projectile should be able to deliver damage predictably, not sporadically.
I bought some 20 grain gamepoints and will see if they rectify the problem.