Similar thing happened to us up at Second Chance earlier this summer. IIRC, the turtle survived for about 5 days after we injected about three times the recommended dosage of euthansia drugs.

Don't remember that one being exceptionally large, though, and she (we kind of assumethat any snapping turtle brought in to us early in the summer is female) certainly didn't every lay eggs.

Kind of makes you wonder just how common this sort of thing is.