November 28, 2014 (edited) , KOに번역する (번역を見せる) , ENから번역されました (원본을 보여주는)
The "X-Rated" level was added only a few years ago, but I remember a bunch of blow-ups on the forums here over some "possible" penetration (by a lotion bottle) in one of the clips of Natalie Blond (Card #a0488) when it first came out. Also, many of the Classic clips have fingering as well.
I think it's almost random whether a clip gets the "Full Nudity" or the "X-Rated" label. At least, I can't really see any difference on the kinds of clips we're talking about.