Well, interesting pickup for Derpy today... He's doing much better, and the shell injury has been filled up with thick skin which is normal during healing. I'll put pictures up later.

He drank some water and is very alert. One thing that worries me, is that when we offered him a blueberry after getting home (mostly to see what he would do) he did the normal turtle "I am Not Amused" gesture of turning around, but his left front and back legs were very odd, and the whole 'turning around' process took about three minutes, even though he was trying hard the whole time. The front leg kept not hitting the ground when he moved it, and when it did, it was almost like he was walking on the back of his foot. The back left leg just ended up stretched out and dragged behind him...

He does have full mobility of all the legs, but if this keeps happening between now and this weekend (release time) I'm going to video it and contact the rescue again...