The problem, I've seen, with the Flickr system is that when trusted users spot a Flickrvio and template it accordingly, they can't delete it, and it goes into the "possibly unfree cat". That cat also contains all the images where the Flickr user has change the image's license (the thing they're not allowed to do but still do), so it's very difficult to check the cat for always-unfree images, compared to once-free images, simply because it's so full.
At least, that's what I've seen. I may be wrong, since I just delete the Flickrvios when I review them.
Solutions to this? I don't know...we need the trusted users to help with the backlogs, but we don't trust them to delete, yet. Create a new category for those they tagged as unfree? I'm sure there are other issues with Flickr license issues, that way.