Well, I can think of two things that happened in your recounting of the broody hen story that may have contributed to the low hatch.
1. Initially, there were too many eggs under her. You did take some away to whittle down the amount, but the damage could have already been done at that point. Maybe you ended up taking away the freshest eggs without realizing it, leaving older potentially more deteriorated eggs under her.
2. You moved her and her nest just a few days before hatching. It might have jostled things around or left her unsettled. I would think that any abrupt change that close to hatching wouldn\'t be good.
I had a broody Australorp hen setting eggs that were due to hatch at Easter. It was the first time she\'d ever set eggs, and she hatched 3 of the 7 put under her. She crushed one that pipped and a fifth pipped but seemed to be dried in the shell. I\'d say she did okay. If it was the first time she\'s set eggs, just chalk up the mistakes to inexperience and the disruptions during incubation.
If the problems had something to do with the location of the nest (too damp or dirty, something like that) I don\'t think you would have had so many make it as far as almost hatching. I\'m trying to figure out the best set-up for broody hens because I\'d like to get away from having to keep heat lamps running over flammable material like bedding. My husband and I built three 3x4 units that are half plywood, half wire so that a broody hen could be enclosed in the plywood side \'til she\'s ready to take her chicks out of the nest to explore. Unfortunately they\'re all three filled with chicks I hatched in the incubator! Maybe a designated broody spot where she can be quietly alone would help. At least that would control for interruptions from other hens trying to lay in her nest and you wouldn\'t have to move her.
What kind of water do you have, well water or town water? When I lived outside of DC there were days where the water reeked of chlorine and we had to set it out overnight to let the chlorine evaporate before it was suitable for baking bread because it would kill the yeast. Maybe there\'s something in your water. Do you have copper or lead pipes if you have a well? If you use rainwater caught in a barrel, is your roofing so new that maybe it\'s leaching something? Just trying to think of anything unusual that might lead to low hatches.