Well, its more an agregate of knowledge from all of the various questions asked and answered. Here’s some official tidbits that relate.
Stacking While Moving: The stacking limit applies only at the end of each player’s half of the movement and assault phase, after all movement and unit placement are finished. Moving units can temporarily exceed the stacking limit during the phase, provided each hex is within the limit at the end of the player’s portion of the phase. If a hex exceeds the stacking limit at the end of a phase, units must be moved back to their previously-occupied hex until the overstack is corrected. These moves are done in reverse order – that is, the last unit in must be the first one backed out, and so on.
WotC_Huscarl
Re: Overstack and no retreat–------------------------------------------------------------------------------
There is only one legal retreat hex for any given overstacked unit – the one that it came from when it entered the now-overstacked hex. The last unit in the overstacked hex must back up to its previous hex.
If that causes another overstack, then it sets off a daisy chain of unstacking. The last unit in is the first one out.
Steve