[Wrana]

IIRC, there are some Greatsword regiments that don't wear helmets, but other do. In 6th ed. armybook I clearly see Wissenland Greatsword in Capellino helmet (p.11), some Greatswords in what is "Iron Cap" (p. 31), Carroburgers with both (p. 42), but Talabheim with no helmet as I see (same page). I don't have 7th ed. one on hand, but I think you will get similar pattern from it.