The reason for the original post was to see if there was any indication that the additive had completely worked.
So for example, if we expect the oil to turn black from carbon, and these are supposedly one tank treatments, then on the first usage, the oil would be black, but on the second, the oil wouldn't be because there is nothing to clean.
On the other hand, I heard that carbon is like a dye, so very little would be needed.
Anyway, I'm just trying to look for secondary verification, beyond the butt dino, that it's worked and the cleaning is complete.
If it's reasonable that a dirty system will turn oil black and a clean system won't, then it might make sense to do one treatment before an oil change, then another after.