This is in regards to Knight-Paladin Gelebor's unique "unobtainable" armor. Not sure if anyone else already knew this, but you can indeed equip his unqiue cuirass through the console command player.equipitem 0200CAD3. It will not show up in your inventory, but you will see that you are wearing it and it has an armor rating of 135 (I assume depending on skills). Just a little side note for those who wondered xD
Unless you put it on a female as i don't think there is a female mesh for it but i don't like the idea of an invisible item in the inventory maybe try adding the item before equipping it (or theres a replacer mod here for the armor).