I think that voices of both Johnny Carson and Sean Connery changed drastically in their later years. This was most noticeable when they pronounced sounds involving "s". A variety of things can cause a change in one's voice. It could be something as serious as a stroke. In the case of Carson and Connery, I wonder if it was dentures. I don't have dentures myself so I can't evaluate the plausibility of my theory. Is it a reasonable idea?