I have similar experience recovering wounded deer having killed probably close to 150 deer and being on hand when close that many have been killed.I also used to be on a committee for a semi-controlled hunt where I was called out multiple times per week over a 10 year period to recover wounded deer.I couldn't even try to count the number of blood trails I've been on but it's literally in the hundreds.I'll echo most of what John said because he's pretty much dead on.My only minor exception would be with gut shots.I too believe the recovery rate should be close to 100%.However,8 hours is not nearly enough time in my experience.It can be,depending on what was hit but if they're dead in 8 hours,they'll still be dead in 15 hours.I've recovered easily over 100 gut shot deer and this is my experience.First,if the hunter backed out and I mean back strait out without even checking his arrow,we recovered 100% of every deer the next day.If the hunter pushed the deer just one time,we never recovered the deer in useable condition.The vast majority of deer were found within 50-75 yards of where the hunter last saw the deer but close to 50% were still alive to some degree 12 hours after the shot.I've seen deer killed with every broad head imaginable and the results were no better with huge mechanicals vs small fixed heads.In fact,the ones shot with big mechanicals seemed to run out of dodge and go further before laying down.I've walked up on deer after 8 hours that took off like they weren't even hit.Today if I go after a gut shot deer,I wait at least 14-16 hours before starting to look.Otherwise,that was the best advise I've ever read on recovering wounded deer.If a deer is hit good,you should see or hear them fall the vast majority of the time,if you don't see or hear them fall,chances are,you didn't hit them nearly as good as you thought.Back out.