On his Wikipedia page, in the 1966 - 1975 section it says it took a lot of persuasion to get him to use the wheelchair. This suggests that he wasn't in dire need of it at that point. His first child was in 1967, the last in 1979.
6. Extremely high ammonia levels in the water can damage the outer layer of skin and cause shedding. RES are tolerant of high ammonia levels while map turtles are not, so this problem is more likely to occur with Graptemys species.
A nest area is very important for her to lay her eggs naturally. If she does not lay her eggs, she might lay eggs in the water or retain them, which would cause egg binding. If the turtle has laid one or two eggs in the water, you still need to provide a nesting area. It is likely that the entire clutch was not laid and she is still gravid. Egg binding, egg retention or dystocia occurs when eggs are abnormally held within the body. These eggs can decay, deteriorate or become calcified.