Well, I completed "House of Pleasure" with absolutely no kills or detections after hours of scouring the map for items. The achievement didn't pop, I checked the description and thought: "[censored]." I do not want to start an entire new game, recollect all those runes and bones, undo hours of work, just to fix a few accidental kills. Now there's almost no point in going non-lethal from here on, even though I really want to, because then I'll have to replay the entire game the same way twice. I originally wanted to play non-lethal, then follow that up with all kinds of brutality. Now it's looking like "Non-lethal with one accidental kill/detection" play-though, "non-lethal clean hands/ghost" play-though, then "cut loose, have fun, and kill everything" play though. Not what I had in mind.
My question is: I noticed that there is a "mission select." If I continue playing from "Royal Physician" onwards without getting kills/detections like I originally intended, can I later go back and replay "High Overseer Campell" though mission select and will that count toward the achievement?
I enjoy non-lethal. I don't kill guards that are just doing their jobs (I've been framed for murder, let's kill half the city. That'll show them I'm not a murderer). I love the "worse than death" punishments. I just don't want to do two non-lethal/ghost play-throughs because of a noob-mistake. One is frustrating enough.