If blades come off it is a sign that they are growing, they have given the stretch, the ones that I have are still throwing sheets at me and they are really healthy.
A few months ago a turtle that I had 20 years old with me (one of the oldest) died, I also have others of 20, 17,15,8 years and all at some time of the year give off these types of sheets, a symptom of what they grow from. .
Another thing would be that they have the shell in bad condition and present decalcification.
Greetings and I hope it helps you