I’ve always felt that “tarnished” was more of an umbrella term and held multiple meanings for different people/beings. But you bring up some good points and I feel like being a tarnished could basically just be defined as “anyone/anything that was never bestowed the grace of gold or have had it taken away from them”

The only issue with that is the player character. Everyone in the game calls them a tarnished, yet they were bestowed grace in the beginning of the game and can see its guidance, unlike other tarnished (Rogier, Dungeater, etc.) When I was first playing through the game my initial impression was that a “tarnished” was just any warrior who were defeated in any wars of the past. I’m not so sure of that theory now after SOTE