I believe you're right about #81 going into the lake Bret. I think she was backing a work train which either hit ice or just simply derailed and pulled 81 (19) into the lake. She broke her crosshead and frame, of which the repairs can still be seen if you know where to look. I don't know if the repairs were made after re-railing her or after she was worked back to Skagway. If I remember right, Ron Brinton posted pictures of that accident on this forum many years ago.
I think #19 also went on the ground in Prairie City once (weird to think the big Alco's used to go all the way to Prairie), and I think she let her passenger train derail somewhere too, though she didn't hit the dirt. J.D. True also told of her running through an open stub switch in Skagway and ending up with all drivers on the ground. Regarding #20 I've not read of any mishaps.