You have what's called a "staggered hatch" going on. That happens when the eggs start incubating at different times. Typically, not all the eggs will hatch, because mama will get off the nest within 24-48 hours after the first eggs hatch. She will do that because when all the eggs start incubating at the same time, anything that's going to hatch will usually do so within that time frame. Something to consider in the future, (or even with your newest broody) is to give her all the eggs you want her to hatch at once, mark them, and daily remove any additions that show up. It may be helpful to have an incubator ready in case mama does abandon the nest with viable eggs still in it. But you may end up raising those babies yourself. Broodies don't always accept new chicks once they have left the nest with their babies. If you do try to give them to her, watch to make sure she doesn't attack them, and don't be surprised if she does.