For what it's worth, it might be good to clarify what is meant by "frontline" and "rear line"
There are really two defintions of a frontline/rearline unit: (1) A unit whose card says "Frontline" or "Rearline" (or both). (2) A unit that is in the frontline or rear line physically.
The reason this is important is that the Shaken card will send a Frontline unit (infantry) back to the rear line. Now, the rulebook says a Rearline unit can attack front or rear line units. So it could be confusing that a unit labeled "Frontline" that is in the Rear line could attack. If you clarify it, it makes more sense that a shaken infantry can't attack, because it's a front line unit even though it's physically in the rear line.
Just a suggestion for something that tripped us up a little bit.