How did you determine that the extra calcium was causing the problem? If a bird has a normal metabolism, unneeded extra calcium should just pass through the intestinal tract without causing problems. Parathyroid hormone and vitamin D are very finely tuned to allow the body to absorb only what is needed, specifically to prevent excess calcium from entering the bloodstream and causing harm.
In a typical 26 hour egg cycle, the shell takes 18 hours to form. During that time, the hen uses 100% of the calcium in her blood every 16-20 minutes. It gets replaced constantly by what's stored in her bones and absorbed from the intestinal system. During the 8 hours of the cycle that she's not forming a new shell, the calcium that's being absorbed is resupplying her bones with the amount that was used creating the previous shell. It's an extremely dynamic system, with calcium being moved from the intestines to the blood to the bones for storage, then from the bones to the blood to the eggshell for use at a phenomenal rate. One of the advantages of oyster shells is that they take some time to break down in the gizzard, so they're in the system supplying calcium even through the night after most of the layer food has moved through.
If there's not enough calcium being supplied through the diet, via layer diet or oyster shells or limestone or something, then eventually the bones will thin in most birds. Some will get away with it long term, others won't. Logically none should, but nature has a way of keeping us going despite logic. But nature did not create a chicken or turkey that lays more than 100 eggs per year. That was done through selective breeding, and was supported by a modified diet that provided the supplies to maintain that production -- i.e., extra calcium. Feeding laying hens a diet without extra calcium is a huge risk, especially as the hens get older.