Brother from another mother, to me and in just my own uneducated opinion;.....you are examining that shell WAAAAAY too hard!! That guy is in great shape......
Turtles are some really tough creatures.....but a band aid might make you feel better.......I'm TEASING.......but 65 folks looked at this before I did and none of them would touch it.....so I figured to have some fun.....LOL
Seriously though, If there is an issue, the guys following me will let you know......
It's a great picture, very easy to see what's concerning you, however, I don't have any words of wisdom for you. It looks to me as if there may have been some damage on the new growth area a while back, but it has now filled in with "blond" new growth. I wouldn't worry about it.