A fully tracked AFV on the road of a woods-road hex attempts to enter a woods hexside of the same hex. It fails it's bog check. Is a trail break counter placed on that hexside at this time?
No.
A wreck or Immobile vehicle on a TB counter removes that TB...
(If the answer is no it would have to take another bog check should it unbog and wish attempt the same move.)
Correct.
Placement of a partial TB effectively means that a fully-tracked AFV has entered the woods portion of a woods-road hex without Bogging, and may therefore exit the hex free of a Bog Check (provided it doesn't make a VCA change before exiting). If the AFV Bogs, no partial TB is placed/retained.
Once on a partial TB, a vehicle may exit a woods-road hex across a non-road hexside without risk of Bog unless it attempts to change VCA before exiting or it enters other Bog terrain.
The rules are silent on what becomes of this partial TB, however. I suspect that it is removed, having served its temporary purpose. IOW, I
think that the sole function of a partial TB counter in this situation is to show that the AFV may leave the hex without risk of Bog. Once the vehicle leaves, the TB is removed.
A Q&A could be in order though wrt to the status of this truncated, partial TB.
A Fully Tracked AFV has entered a woods location, placing a partial TB counter and ending its MPh in that location neither immobilized nor as a wreck. A second fully tracked AFV wants to enter the same woods location via the partial TB with the intention to end its MPh there as well. Can the second fully tracked AFV use that partial TB free of a Bog check? Could the second AFV “complete” the partial TB by exiting the woods hex?
A. No to both (B13.4211-.12); place a second partial TB when the second AFV enters (unless the first AFV had bogged, making it Immobile and removing its partial TB).