Partially hatched or unhatched eggsIn the wild any late hatching ducklings that are not yet out of the egg or are just too new to leave with the rest will die of starvation unless a predator eats them first. One of the hard parts of providing nest boxes is that I prefer to euthanize the late ones. I do it very quickly with no chance of awareness at all for the little duckling: just an instant "lights out".
Unhatched eggs are also a concern. In some cases the unhatched eggs are infertile but in others they were laid by other hens after incubation began while the incubating hen was out to eat, or they were unnoticed in a cold corner for a while. In either case their development was delayed.
Therefore some unhatched eggs contain a live duckling that is a day or more behind those that left the nest. In the wild these would either hatch late (and then starve) if they are close to being ready and the weather is quite warm, or if that doesn't happen they would get cold and die still in the egg. Nature can be harsh.
If I put unhatched eggs directly into the garbage and if it's warm in there I could end up with little peeping sounds from the garbage can a day or even several days later. Oh no! To avoid this in a humane way I put the unhatched eggs in a plastic bag and put that into the freezer for a day before putting them in the garbage can.