What to do with eggs that were "snuck" in?

You can figure that the hen will leave the nest within 24 to 36 hours of the first chick hatching. You will have to either incubate the eggs or toss them. This is why I try to make it impossible for hens to infiltrate a broody hen's nest.

 

I would toss the unmarked eggs and start checking the nest daily for extra eggs.

 

Don’t throw them out. If you have an incubator, you can hatch those too.

My broody collected eggs and I also lost the markings. At first I just took away the eggs that I knew were snuck
In the nest, but once the markings were rubbed off, I had no clue and we were already around day 15.
On day 22 I took the eggs and put them into the incubator. She got day old chickens instead to get her off the nest already. She was sitting for months and couln’t hatch a thing. First timer. Anyway

After 4 days I candled to see if there were any unfertilized ones. I threw those out. I floated the rest that I was not sure of, I didn’t float those that were obviously moving. I left them in the incubator without turning since I didn’t know if any of them were in lockdown stage or not.
On day 31 and 32 I had two chicks and today is day 35 and one is zipping. I am watching this one because it is zipping in the wrong direction and I think it will get stuck.

I had 4 eggs left and one I was not sure about since the float test was iffy too but it is so dark in the egg I can’t see anything, I know there is a full grown chicken in there. Once this chick hatches today, I will float the last one again and go from there. It has been long enough for a full grown chicken to hatch.

One problem I have now is that the broody is already happy with the chicks she has and she rejected the little one I tried to sneak under her a week later. The original chickens were 9 days old and the new one was 2 days old. She did not accept it.

So I will have 3 chickens grow up without their mom, but it’s a good problem to have: I have more chickens than I expected. It is summer time and I can leave them in a chicken tractor or in the shed and integrate them in September before it gets cold at night.