As someone who has hatched eggs, I question this story. Eggs need oxygen just as much as the next animal does, that is why the shell is permeable. With no umbillical cord connected to mother to deliver oxygen (which mammals get), the chick would suffocate.
Not only that, but hens impacted with eggs don't generally die from 'wounds', but rather infection from having a foreign body wedged in there (which would have happened well before 21 days). Newborn chicks are exhausted and soft when hatched, not something capable of tearing up anything after they are done fighting with the eggshell for hours on end.