Its interesting so few of the designs have taken a stab at the larger great powers of the war. Germany, Britain, France, Russia, and the Ottomans, not represented yet. Only the U.S., Italy, Austria-Hungary, and Japan. Very fascinating.
My bet is that save for France and Britain (and Britain's a bit iffy on those regards), all of those were represented as actual mods, while Austria-Hungary is the only of the latter you mentioned that has become a mod.