I suspect that the deal is they keep 2257 records for the explicit stuff, and no records for the nonexplicit stuff. Their index page for girlsgonewild.com isn't even compliant! There's no 2257 notice until you get inside the site, and they have language indicating that some of their content is exempt, which is what leads me to believe they keep no records on the girls who flash tits and do nothing else, meaning, they have no way of knowing whether the girls are of age or not, unless they shoot explicit content of them.
Mind you, this is conjecture, but they've never claimed to have docs for all their girls, only that they are "completely compliant."