Small update...I was in the coop one evening before "chicken bedtime" to make sure they had water, it wasn't frozen, etc, and while I gave them some veg, I noticed one of my mixes was just standing in the corner, fluffed up. I was concerned, because I thought she was sick, and than she laid a completely shellless egg...NOT the chicken I has suspected. This girl is the biggest of all of them.
It was apparently not the first time, as the barred rock was standing next to her, with her head right near her bottom, and as soon (or maybe before!) it hit the ground, the BR had broken the egg and four chickens started eating it immediately.
As far as I'm aware, they've never eaten the shelled egg. I upped my calcium to them, by giving them oatmeal in milk & yogurt with oyster shell and powdered milk, for two days.
Now for three days straight, I'm getting a SHELLED (somewhat thin, but not paper thin, maybe grocery store thin) WHITE egg, in the same box the shellless and thin eggs were being laid. It's mishappen a little, like a small perfect egg, with a bulge on one end. I'll take some pics this afternoon. It also has..scrapes in it, as if someone had run their nail down it, and left an impression. All three eggs have 'scrapes'.
I'm sure I'm over-thinking it.