For me, awarding unadjusted XP makes more sense because it covers partially successful encounters and layered encounters.
Suppose six bandits is a medium encounter, allowing for the x2 because there are six. Encounter 1 is with six bandits defending the outer walls of a fort and Encounter 2 is six more bandits defending the keep. If the encounters were unconnected, you could do the XP either way and it wouldn't matter much apart from rate of advancement. Each encounter is worth something and they are both worth the same.
Now let's connect the encounters. In encounter 1, the PCs kill three bandits and the remaining three retreat into the keep. You now have three dead bandits and nine live ones. The PCs shoot some arrows into the keep and kill one bandit but then decide not to storm the keep yet because it's obviously too strong. (You know that, because if six is medium, nine is deadly; and maybe they know that too).
How much XP do you award? Four bandits killed is worth 4 bandits. The first encounter is not worth 6 because the other three weren't defeated - they are still there, in the keep and still a threat. It's not worth x2 because the PCs didn't defeat all six. And what about Encounter 2, if the PCs come back next session and take on the keep? Do we recompute it x2.5 because there are now eight, or is it x2 for the original six and x2 for the extra three? And was the one that was shot in the keep one of the three who retreated or one of the original defenders of the keep? It's a nightmare to calculate.
Much simpler just to count the dead ones, regardless of which encounter they were in. You understand it, the players understand it, and everyone is happy.