I experienced this years ago using round ball but lately using Maxi hunters in my flinters and Hornady XTPs and Harvester sabots, I have excellent blood trails.
I am glad to see you are persistant in tracking your animals and recovering them. There are quite a few so called 'hunters' out there that shoot and either don't check for sign of a hit because the animal didn't go down, or look a bit, don't see any blood and figure they missed.