Was there such a thing as a XX porn?
X, yes... usually soft core porn or exceedingly violent exploitation schlock. Some real movies released with this rating like Midnight Cowboy, though, which won the Academy Award for best picture. Later changed to NC-17.
XXX, yes... asses blasted, just don't get it in my hair, good ol' American hardcore.
But XX? Can't say I ever came across such a thing. You?