inability to select any lemmings buried in terrain
I was mistaken on that point. Maybe the first time I tested it on some earlier level the lemming was too close to the top or something. Anyway, as long as you selected a skill type that can be assigned to the lemming (floater and bomber are good options), you can still highlight a lemming buried in terrain, and assign skills to it.
So, I was able to track the movement of a stuck climber now. It basically moves upwards just like in original Lemmings, but with the additional rightward drift. I guess there's an asymmetry when facing left and facing right that ends up moving the stuck climber lemming steadily rightward. (
I can't quite tell for sure yet what exactly is the asymmetry.)
[edit: I have identified the asymmetry that allows the stuck climber to gradually drift rightward. When the stuck lemming "falls", "lands" and turns left, he immediately starts climbing again. But when he "falls" "lands" and turns right, he can walk forward for one grid-cell before starting again to climbing. This extra bit of walking allowed only when facing right, results in the gradual rightward drift.]
[edit2: note that when a stuck climber falls and turns left, I mean it when I say he
immediately starts climbing. It appears the transition is directly from faller to climber, making it impossible (in all my tries so far) to assign skils to a stuck climber facing left. For a stuck climber facing right, you can assign him skills during his "extra walking" phase.]