I shot a doe last year and thought I had gotten poor penetration. The arrow stayed in for a while, but was hanging out and flopping when she ran.
After recovering her a short distance away, I found during field dressing that the broadhead (Snuffer 160) had penetrated to the opposite shoulder and the tip had curled. The arrow apparently "bounced" back, causing it to look like penetration was bad even though the arrow had done its job.
I don't stop deer, either. I want them calm and unaware.