How to tell if late stage embryos have died

[RedOkra]

I have a sitting hen - I have no idea when she started sitting because I was not intentionally trying to hatch out eggs, but I know its been over two weeks, and I think I'm past 20 days now. There was one morning when there was no hen on the nest, and I'm just wondering if there is any way to identify dead embryos once that are late stage. Do they still get a blood ring?

 

[SpiritedFarm]

I dont think they do, I think the blood ring is a sign of death in early development.

Late stages I would watch for egg movement, or you could candle and look for movement?