So when a hunter kills any animal (deer/wolf/boar) and then collects the carcass, it will show up as a carried item in their inventory. However if any new command is issued other than taking that carcass back or collecting another one, the one in the inventory will simply vanish. This includes attacking another animal, commands from the player, retreating, etc.
This means a hunter can kill a wolf and collect, only to see another wolf approaching whereupon he will discard the carcass and attack the second wolf. He will then kill the second wolf and collect only to notice a third wolf in range that hasn’t even spotted the hunter yet, and then choose to attack the third wolf, losing the second carcass in the process.
I have watched as one hunter can go through five wolves to only bring back one carcass, and yes only one gets butchered (watched the hunter shack to see if multiple would show up). The others disappear into the void. I also know that hunters can carry multiple, or return to collect others, if they kill all the animals before doing any collecting (so all are still available to collect).