Eggs Not Fertile or Dead in Shell?

I would really like to know more about how to tell if the eggs are
infertile or dead in the shell. I am sure that most of your breeders
probably already know this information so I am not sure if it would
make a good article or not. If there is a previous article that you
would recommend me purchasing please let me know. Thanks. Paula :0)

Not sure if an article is warranted or not but I can tell you the following:

Eggs do not candle fertile until they are a week old. If the embryo
dies before that time there is no way to know if it was ever fertile or not.

Once the embryo starts to develop, if it dies before the chick is
formed, it will be reabsorbed into the yolk sack. If you are checking
the eggs daily, you will see it as fertile then it will 'go blank'. If
not, it will usually be re-absorbed within 24-48 hours so you might
miss it if not checking daily.

If the embryo fully develops but dies late in shell, then you will be
able to see the dead embryo.

Hope this helps!