But given that so many models at GDP are 'one and done' I suspect that there is no exclusivity contract. It wouldn't make sense for either party. If the girl was exploring the possibility of getting into the business in a professional way there are lots of sites that would pay for that. I doubt that a model who wanted to explore that as a career opportunity would be willing to say that she'd not work for anyone else. That would end her career even before it started. From the site's perspective it wouldn't make sense either. Having the first scene of a popular model would drive business to GDP. If I discovered a model I like a lot did her first scene at GDP I guarantee you I'd join to get that scene. I can guarantee that because I've done it in the past.
I think the most likely reason that the girls on GDP never pop up anywhere else is because they want to experiment a bit and have no intention of doing anything else. Other sites feature models like this too - Exploited College Girls is another good example.
On a darker note, I have read that GDP may use some deceptive practices such that the models want to experiment a bit but aren't told it's for a well-known site. There have been allegations that the girls think the scenes won't be on a site or if it is it'll be on some obscure foreign site.
Bottom line: I admit I'm only speculating, but I think it is unlikely that the girls who appear on GDP are contractually prohibited from appearing on other sites.
[Link]