I have not noticed that messing the regular layers up. Many pullets get the hang of laying in a nest right from the start but some have to lay a few eggs before they get the hang of it. They can drop an egg from the roost or wherever they happen to be walking. Sounds like you are aware of this.
One time a fake egg got scratched out of a nest onto the floor of the coop. That's where I learned I needed to raise the lip on the nest to make it harder for them to scratch eggs out. Another hen that regularly laid in a nest laid her egg that day next to that egg on the coop floor. When I raised the lip and put that fake egg back in the nest she went back to laying in the nest. I don't know if something like this was going on, either scratching the egg out or laying next to that one in the corner.
Not in my opinion. Mom would toss her eggs cracked in half where the chickens could get to them. They never had an egg eater. I tossed my egg shells (not crushed) onto the compost pile where the chickens could get to them. They did not always eat them, they were getting enough calcium elsewhere. I had an egg eater but that was after I'd stopped free ranging and fenced them away from predators and the compost pile. I think what started her to open eggs to eat was a pullet laying an egg from the roost and it breaking.
Some people crush them and offer them back. Some people bake egg shells before crushing to cook any raw egg that might be on them. I don't consider either necessary but that's just my opinion. Both are common practices on here and I don't see anything wrong with them. Don't be surprised if they don't eat the egg shells. Some don't.
