The ones that did hatch yolky and bloody typically survived with some doctor care from me. But I got tired of their lives beginning that way so I just decided not to use those eggs anymore. They were older hens which I'm sure had something to do with it.
Very interesting and useful post! Yes I have found that the eggs you put in are pretty important too. Last year I had two hens that always laid abnormally large eggs. The chicks were fine until they started hatching. In those eggs they always started hatching out when they clearly weren't ready...