On the contrary, I think that it is strongly implied that Uther is the only one. He was not the first nor the last person (or even paladin) to get killed by Frostmourne. If such split had occured before, they would have noticed it in Bastion on other aspirants. Or other covenants would have noticed it. Yet, the idea of souls being lost to Frostmourne, a weapon from the Maw, on the mortal world is something totally new (and unthinkable, it seems) to all Kyrians except Devos.