There might be two clutches in there - one that was laid several weeks ago and failed to hatch, and a new one that was started recently and is fertile. If that's the case, some more eggs may appear before it's all over. If you put marks on the existing eggs, you will be able to tell which eggs are newest if more appear. Use a felt tip pen on the big end - the tip is soft and won't damage the egg if you're gentle, the ink is nontoxic, and that end has the air cell anyway.
If too many eggs accumulate it might be difficult for the parents to keep all of them warm, since they only have so much body surface to put on top of the eggs. Within a few days, you will know whether any of the current eggs are infertile. At that point you can remove the infertile eggs if you think there are too many eggs in the nest.