Four months after taking this photo above, I looked at it again.
And I thought, "Well, you know, that's interesting: the numbers involved all may work out realistically or anatomically correct, turtle shell-wise: 13 scutes, 13 moons, and 13 stones."
Like figuring out where all the loose pieces of veneer go back onto an inlaid table top on some fancy piece of antique furniture - or doing a puzzle with my mom or my granddaughter - something about the shapes of the stones mimicking the shape of the scutes just "clicked" and I think I can see how this testudinate petroform goes back together.
Who took it apart, when and why, I don't know, but I can see the order in which they may have removed the stones. I'm sure they got nothing but bad luck and trouble in return.
I might have the numbers wrong, maybe there's left and right 1 thru 4 (sinister and dexter) pleural or costal scutes, but I think I get the idea...