Having trained in Yoshinkan for quite a few years, I know Kancho's definition.
Atemi - strikes to vunerable parts!
Like I said, pain is not the goal. A KO can be the goal and whether the recipient feels pain or not is irelevant - they are KO'd!
Don't get caught up in pain from atemi. It is analagous to treating the symptom, not the cause - looking for a side effect, not the result!