Ty got us answers to your questions before I even saw the thread. :-)
Rule 12.22 probing attacks and rule 12.24
Can you make a probing attack, per rule 12.22 with the Third Army Four Corps Stack and then use rule 12.34 (Special US 3rd Army Advance After Combat) to advance bonus hexes?
You can still make a probing attack if you are adjacent to an enemy unit? I assume it is a means to 'infiltrate' a line rather than attacking the enemy unit directly. Perhaps to help set up a later phase concentric attack?
Thank you for your questions, sir - all of these clarifications will be incorporated into the rulebook when we do the revision.