Talk:Clean Hands/@comment-187.172.184.126-20121119213825/@comment-5469467-20121210040346

According to the details of the Dishonored 1.2 Update on Steam, this was one of the features:

• Fixes for some interactions with Granny Rags that invalidated nonlethal playthroughs under certain circumstances. (Note: These fixes work even for savegames AFTER the final Granny Rags encounter.)

I myself finished the game wthout killing anyone, but this was not recognised for the achievement. After the update, the achievement was unlocked when I reloaded and finished the last level. Problem solved!