YOu probably have a bad egg. They will sometimes look dark like there is growth. But you should be able to tell a couple of ways.....first of all, a non-growing egg does not hold heat.
Also at day 23, if anything is alive, you can tap on the egg while holding it to your ear. You will 9 times out of 10 hear the chick scratch back.
Lastly, what I do, when i doubt, is take a very sharp object and carefully poke a hole in the top of the egg. I clear away a bit of shell and look to see if the chick is alive or not. If it is, then take note if the veining has retracted and if the chick has pipped through the membrane.
Yes, you do risk shrink wrapping, but some warm water and a bit of time helping the chicks is better than a dead hatch.
I would be careful of the "smelly" ones. If you do have a rotten one, it will be horrible when it explodes. Check to see if any of the eggs are weeping or oozing. Throw them away immediately - outside. You do not want one of those to explode on you or in the house. it takes forever to get rid of the smell.