Just maybe to give a clue as to how resilient baby chicks can be 
even before they actually hatch.
So, I was unexpectedly absent for a couple of weeks and had a few friends come daily to feed the chickens and collect the eggs. One of them also has chickens and said that one of mine seems to have gone broody and they just left the eggs that were under her in a nestbox, not marking any of them or making sure they were collecting any new ones. So when I came home I found a newly hatched chick, the hen was still on the nest. By the next day she had left with the one chick, but one more chick had internally pipped by then. I took the remaining 4 eggs inside and placed them just above the wood stove, so they kept warm. No temperature oh humidity control whatsoever. By the evening, the chick pipped externally. I placed the eggs under broody overnight and sure enough, the chick had hatched by morning... It had trouble keeping up at first but cought on pretty quickly.
I felt bad for the remaining unhatched chicks (all of them still alive and pretty far along) but had no capacity to uncubate them and take care of them myself, but also I felt bad just tossing them so I just left them where they were. Not having any hopes for another one to hatch successfully I could hardly believe my eyes and ears when 5 days later (the nest was not attended during the day with temperatures about 15°C, the broody was there for like 13 h during the night though) another chick pipped. I did the same thing - took it inside to warm up, put it under broody during the night. By morning I found it had hatched but was already dead in an empty nest. I was not there extra early and am not sure what happened. I am also not sure why I hadn't removed the remaining 2 eggs... But a day later (so 1 week from the 2nd chick) I found another pipped egg. Sceptically, I took it in and just made sure it was warm. By the evening it had almost zipped and it hatched under broody before I went to sleep. I made sure I was there extra early in the morning though, to take it inside if he was left in the nest.
So now it is day 3 since it hatched, the first 2 we kept it inside in a improvised brooder and moved it to his mum overnight. Today I put them all in a separate coop to see if the chick will accept his mum and vice versa. The little one is a bit confused, mum also, but less so and seems to have accepted the 3rd chick with no problems.
...I know the chick 2 and 3 probably would not have made it through without my interference, but on the other hand, it seems to me they have hatched against all odds, at least the 3rd one
even before they actually hatch. So, I was unexpectedly absent for a couple of weeks and had a few friends come daily to feed the chickens and collect the eggs. One of them also has chickens and said that one of mine seems to have gone broody and they just left the eggs that were under her in a nestbox, not marking any of them or making sure they were collecting any new ones. So when I came home I found a newly hatched chick, the hen was still on the nest. By the next day she had left with the one chick, but one more chick had internally pipped by then. I took the remaining 4 eggs inside and placed them just above the wood stove, so they kept warm. No temperature oh humidity control whatsoever. By the evening, the chick pipped externally. I placed the eggs under broody overnight and sure enough, the chick had hatched by morning... It had trouble keeping up at first but cought on pretty quickly.
I felt bad for the remaining unhatched chicks (all of them still alive and pretty far along) but had no capacity to uncubate them and take care of them myself, but also I felt bad just tossing them so I just left them where they were. Not having any hopes for another one to hatch successfully I could hardly believe my eyes and ears when 5 days later (the nest was not attended during the day with temperatures about 15°C, the broody was there for like 13 h during the night though) another chick pipped. I did the same thing - took it inside to warm up, put it under broody during the night. By morning I found it had hatched but was already dead in an empty nest. I was not there extra early and am not sure what happened. I am also not sure why I hadn't removed the remaining 2 eggs... But a day later (so 1 week from the 2nd chick) I found another pipped egg. Sceptically, I took it in and just made sure it was warm. By the evening it had almost zipped and it hatched under broody before I went to sleep. I made sure I was there extra early in the morning though, to take it inside if he was left in the nest.
So now it is day 3 since it hatched, the first 2 we kept it inside in a improvised brooder and moved it to his mum overnight. Today I put them all in a separate coop to see if the chick will accept his mum and vice versa. The little one is a bit confused, mum also, but less so and seems to have accepted the 3rd chick with no problems.
...I know the chick 2 and 3 probably would not have made it through without my interference, but on the other hand, it seems to me they have hatched against all odds, at least the 3rd one
