It really depends on what blend you are referring to. There is a Green River Cavendish that is added to a lot of Virginia blends and even Haddos Delight has it. Sometimes it's used for sweetness, sometimes for strength.
I think the fine line of difference in a stoved Virginia and a Cavendish is the sweetener, pressing, and fermenting process. Most of the time I just think of stoved or flue Virginia as just seasoned.
But again, I think it depends of which blend.
Edit: I missed the word "unsweetened" in your question. Hmmm, I would have to say that if it is unsweetened, I have no idea... Maybe they use Splenda® or Aspartame, ha ha!