Sorry to hear your story. Ive killed a few bears, lost a few too, and been down dozens of bear blood trails. I would have thought you had made a perfect hit there.
Instances like these are why Im such a believer in big two blade broadheads lik the simmons tree shark. I figure the bigger the head, the more arteries cut, and better blood trail as well. The Ashby studies want to force smaller single bevel heads on us to penetrate heavy bone but our odds are far greater to hit liver, gut, or any other place than the shoulder bone. And I seriously doubt my recurves will push anything through a bon as heavy as a bears.
Again, sorry you lost him. I dont think you did anything wrong there.