I was just thingking of the following: in light of the rule explaining stacking, I was thinking that at times it might be a useful tactic to deliberately stack an unsupplied unit. This will allow the phasing player to move it to the destroyed units box rather than a possible surrender at the end of the player turn or on the opponent's next turn.
I'm taking this to represent an unsupplied unit being airlifted out or something along those lines.
Might I also suggest to add the following pharse to the rule book: "If the phasing player chooses to remove an unsupplied unit from the overstacked hex, it is moved to the destroyed units box". (It now reads "unsupplied units are moved to the detroyed units box" , which is a bit ambiguous. Itmight be understood as: "a player removes a unit of his choice and IN ADDITION any unuspplied units in such a hex are removed". At least I don't think the latter interpretation is correct and the suggested addition would point this out beyond any doubt.
Yes this is legal and intended. It's not really an "airlift" but a pocket too large to be fully contained, so some parts of units are able to escape (they are destroyed instead of eliminated). In a "you move - I move" game system some fudging like this is needed, especialyl with turns of Two months duration: you can also supposed that parts of those units were able to run away BEFORE the pocket was fully closed.