Hi,
In the Fallen Realm book, the king has a flag on his back and a sword. They represent the Chieftain with a spear and bow.
I suppose you can use both models for either the King or Chieftain.
BTW, in the "Unofficial lotr collectors guide", there's no King miniature. The two minis with the flag and sword are from the blister "Haradrim Horseman Chieftain F&M", and the mini with spear and lance is "Haradrim Command Champion" (from "Haradrim Command" and "Haradrim Commanders").
I hope this helps
Sorry for the poor English