My guess is that on your buck you nailed the shoulder blade.Maybe one lung if you are lucky.Your shot was to far forward.On deer with out a low exit sometimes blood trail are slim.What blood you had was mostly from the muscle tissue not vitals.I shot a doe last year quartering away and had a complete pass through.We never found blood untill we found the deer dead 100 yards away,and the shot was perfect.On your friends doe it could have been a good hit.Last Saturday I tracked a deer for 500 yards.The shot was a complete pass trough slightly quartering with a low exit right at the opisite leg.Infact it passed through the rear of the opisite leg.The arrow was covered in blood.There was no blood trail for five or six yards than mega blood every place.There also was times we were on our hands and knees searching for the faintest blood.We gave up on blood trailing the deer when she crossed the road into open fields.There was a small wood lot in between the fields.We thought for sure she had went in there to bed.We gave her an extra hour and searched the wood lot.No deer.We found her another 300 yards away floating in a large creek.It took us forever to get her out of there.When we look at the shot placement,it looked perfect.When the deed was done we found that some how the arrow had only clipped the first lung and passed through the secound.The angle was just off enough for only one lung.Looking on the outside you would have bet money on a double lung shot.That deer had traveled over a quarter mile on one lung.So never give up on a deer if you know the shot was there.It is around someplace,just not where you think it is.