I've only been raising quail for a few months, but I have a theory that the longer a chick remains in the egg, the more bone and joint problems it will have. Could this be why your late hatch resulted in straddle legs and poor constitution, I wonder? So far in my experience, the chicks that hatch on day one are healthy, but the stragglers that hatch the next day have curled feet, crooked toes, etc. In one case, I had to peel the shells off of some coturnix chicks that had pipped 48 hours prior. Most of these chicks were already dead, but I found a few survivors with very stiff necks and curled up feet. They hobbled around as best they could and the joint problems improved after a few days. They grew more slowly and took longer to feather in though. As adults, they appear normal except that they are less than half the size of the birds that hatched on time.
I believe that the accepted theory is that chicks with joint problems have trouble hatching, but I keep wondering if the cause and effect aren't actually the other way around?
Sorry, I know this doesn't help. My own Texas A&M coturnix egg hatch (55 incubated, 6 surviving) was a dissapointment, so I think the thing to do is just try again with another batch of eggs if possible.