The stingers are very similar to Bear Razorheads. Good choice.

One possible explanation is that even though the deer was broadside, and even though you hit it well, the arrow may not have passed through totally broadside. Maybe the animal moved right as the arrow hit, or maybe a rib deflected the arrow path, you get the idea. So the entrance woundmay be right behind the shoulder, but the wound channel may be angled way back, not your fault and you'd have no way of knowing that happened.