This is an important point. Two others; one big, one small:
BIG: iafd doesn't cover loops ( http://en.wikipedia.org/wiki/Porn_loop ) or their descendents, internet scenes, unless they were eventually compiled into a movie. I would expect 'one scene and out' performers to be more common at the lower end of the market (not shrewd/no body of work) and most of that is going to be internet.
small: The fact that porn tends to cluster around samey names, plus the fact that people who are just dabbling in porn don't put a lot of thought into their names means that a lot of one time performers end up accidentally rolled into another performer's filmography.
BIG: iafd doesn't cover loops ( http://en.wikipedia.org/wiki/Porn_loop ) or their descendents, internet scenes, unless they were eventually compiled into a movie. I would expect 'one scene and out' performers to be more common at the lower end of the market (not shrewd/no body of work) and most of that is going to be internet.
small: The fact that porn tends to cluster around samey names, plus the fact that people who are just dabbling in porn don't put a lot of thought into their names means that a lot of one time performers end up accidentally rolled into another performer's filmography.