Thanks for the answers here so far, keep it coming!
I think it’s really hard to verify the status of copyright given sentences, no matter if they are in the same order as submitted or not. Eventually after reviews there might only be a few left in the queue, and getting harder and harder to identify.
I think copyrighted sentences shouldn’t be downvoted one by one, they should be reported (for example here), and we can delete all of them at once.
In any case, reviewing by submission and not for the full user is IMHO better for that case if we want to go down that road. I’d say it’s more likely that a submission is from the same source, and not necessarily all sentences from a given user. But again, I think copyrighted sentences should be able to be reported and we take care of it to make sure we can delete all of them and do not miss any.
@irvin can you elaborate on that? Reviewing by submission would be new, so I’m not sure what you are referring to as “keeping it”. What exactly is confusing contributors?
We also have some posts on Discourse with review guidelines which could be linked there. I think that would be a good thing indeed, but that will require l10n infrastructure to be set up. Edit: might be tricky though, as this would need a mechanism to create that message, but it’s bound to the language you’re submitting for, not necessarily for the language of the GUI.