Thanks for asking the question.
We have to say the responsibility is on the mod creator to make sure the model they are using is truly legitimate, and that the person who originally created the model, really gives their permission for other people to use it and modify it.
It's quite distressing for the reviewers to have to reject a mod, that someone has done a lot of work on, but forgot to verify its legitimacy before they started. Also there are so many mods coming in and we are providing a free service, it's simply not possible for us to do a full police style investigation into every mod that is submitted.
Other problems we have encountered, people lying to us, taking mods from websites and claiming that they created it themselves. Copying and pasting text from other mods that were submitted successfully, in the hope that it will help their mod to pass the acceptance stage. Other problems too. People submitting a mod almost immediately after importing the mesh, and with no attempt to get anything right, so we end up forced to give them a tutorial through the mods "needs changes" system and repeated submissions. It's quite tiring. I think the reviewers may have been hoping for people to be creative, careful, trustworthy, which of course we do see!
I don't know if the initial rush will die down. I really hope so. We think a mod is something to work on for weeks or months. It should be about quality, not quantity. The reviewers would love it, if fewer, higher quality mods arrived, well researched and tested, with any sources verified and legitimate. Some of the mods arriving are so badly flawed, we have no idea why they have been submitted at all. We may download, test, get a sinking feeling and think, right, where do I start, can the user who submitted it really not see the problems?
Having said that, we have seen a lot of super mods and it is really great to see that. I must admit that I'm struggling at the moment to see how we will get the process working properly as time goes on. Maybe we will have to become far stricter. We really can't just run a distribution service for stolen goods! We want to be a hub of creativity and fun.