Well I know for certain that the "smoke stains" aren't a good indicator on el84's. I had a box of them, given to me by a guy who was looking for the perfect quad. Maybe twenty tubes. Most were reported to have only a couple of weeks of use on them. Many exhibited "smoke stains" on the glass near openings in the plate structure. Even those tubes played long and well for me in a combo amp.
I don't think I've ever seen a dulled or blackened getter. Not that it doesn't happen.
Just my own observation, but it seems to me that the shiny "getter flashing" seems to evaporate with age in some tubes. As I've noticed that many used tubes with a small patch left seem to be at or near the end of their life.