I regularly butcher pullets and older hens that are still laying. I often find an egg still in the shell gland that has not yet been laid. Some are pretty thin. I just rinse them off and set them aside to be eaten within a day. The only development that hasn’t happened is the shell gland has not completely finished adding shell material, the brown coloring on top, or the bloom when it is laid. The nutrition part of the egg is complete once they start putting the shell on. That’s why I eat them within a day, they don’t have the bloom to help keep bacteria out. Personally I’d eat those eggs but do what you are comfortable doing.
It’s good to hear you are seeing some improvement with the oyster shell. I hope that solves your problem. I don’t know how long it takes for that to have a big effect, I’d think you should see a big difference in the next few days if it is going to be the answer.