as an experiment, I had left a pair of eggs in the substrate in the mother's vivarium. they were right next to the glass and could even be candled. I pulled them about 1/2-way as I could see very tiny striations in the shell and was concerned.
6 weeks later, one egg hatched out 100% normally.
during that 6 weeks, the other egg on a couple of occasions would swell with growth and leak a tiny bit of egg white. I was concerned that the hatchling inside would become dehydrated, or that microbes would crawl inside through the cracks and mold out the developing baby. however, s/he hatched fine about 4 or 5 days after the first egg from that clutch. the baby is smaller than the other, but very vigorous. it is now almost 6 months old and is thriving, although still smaller than it's clutchmate.
I could candle the egg and the hatchie always looked good inside, with movement in the last several weeks like any other egg.
whatever you do, don't cut or throw out eggs until you're absolutely CERTAIN the baby inside is dead! if they mold, move them away from healthy eggs but don't toss them or cut them until it's really, really obvious they're duds. sometimes eggs will look pretty pukey on the outside, but the baby inside is doing just fine and only needs to be left alone.