I have 101% overall.
Typically I hear of the achievement popping early when people collect a bandage more than once due to the respawning bandage glitch (You pretty much get the bandage but the game doesn't realize it enough to take it out of the stage or mark it off the map.. so it still puts it in the level but also gives you the bandage for your total) which boosts their overall stage completion above 100%.. or at least it used to. I'm almost positive this has been patched now.
RIDE THE HYPE!!