An amazing discovery today! Becky came over to pick up one of the EEs and the Delaware, and naturally, the two that we wanted had squeezed into a gap in between the coop and the block wall. It was a good thing that this happened, because there was a hidden nest between the coop and the wall that had six eggs in it. I had the gap blocked off with wire, but obviously I hadn't done a good enough job.
I'd last looked behind there about a week ago, and there weren't any eggs, so I had a rough time-frame for how long they'd been there. So, I gathered them up and as soon as Becky left, I went into the bathroom to candle them. 5 of the 6 eggs were developing. And not just a little bit, they were at least a week along. So I marked them, differently from the other eggs, and tucked them under my broody. I don't know if they'll hatch or not, but I figure that is the way that they have the best chance.
This clearly wasn't a broody's nest, the eggs were haphazardly arranged and I'd seen all of my chickens out in the run and acting normally. Where they were, they were shaded by a orange tree in the neighbor's yard, as well as some ivy on my wall, and the radiant heat from the coop and the wall (both of which are cinderblock) would have kept them from getting too cool. I don't know if they'll hatch, but it'll be interesting to see what happens.