Sorry for your loss
It may be helpful next time to make a list of the chickens for head count? With colors/identifying marks?
I farm sat for a farm with over 100 horses on it (miniature horses). I had to do a head count at each feeding, and check it off on my checksheet they made for me. For such a large operation, they had one of the best systems for farmsitting (a checksheet I used for each feeding that helped me make up all of the feed, count heads, feed in order, etc etc etc). I'd just make a check as I completed each task.
One of the best lists was a lists of the "head count" - a separate sheet that stated the color and name of each horse in each pen. So, I could count 27 heads, and if all was good, then good, but if one of the heads needed care, I could go to my sheet and find "White with a brown face, small star", and know who it was, and if they had special instructions.
If he's going to let them out, he needs to know how many need to get back in, and the colors of them, in case someone is missing - makes it easier to hunt them down. Hopefully you don't lose any more in the future!!!

It may be helpful next time to make a list of the chickens for head count? With colors/identifying marks?
I farm sat for a farm with over 100 horses on it (miniature horses). I had to do a head count at each feeding, and check it off on my checksheet they made for me. For such a large operation, they had one of the best systems for farmsitting (a checksheet I used for each feeding that helped me make up all of the feed, count heads, feed in order, etc etc etc). I'd just make a check as I completed each task.
One of the best lists was a lists of the "head count" - a separate sheet that stated the color and name of each horse in each pen. So, I could count 27 heads, and if all was good, then good, but if one of the heads needed care, I could go to my sheet and find "White with a brown face, small star", and know who it was, and if they had special instructions.
If he's going to let them out, he needs to know how many need to get back in, and the colors of them, in case someone is missing - makes it easier to hunt them down. Hopefully you don't lose any more in the future!!!