It really isn't fair but it's going to happen. I've found a lot of things to be unfair about these contests, like people who took an idea and composition from another artist and just replicated it get into the semi-finals over me and other more original artists. It can be frustrating.
There's really no way to know if other people just took work they had yet to submit and threw it into the contest either. It's not fair but it's not worth fighting unless it's really bad, like plagiarism or something.