That pendant was shown for a reason, and we have yet to see the reason. For now I'm taking Corso's word that he is indeed Corso and 1 looks like him through surgery. So who is 1?
I'm pretty sure they explained the reason. The Raza attacked, took the weapons from, and destroyed the actual ship that was coming to help the mining colony, which is how 1 ended up with the pendant. It was taken from the actual ship.