I haven't noticed anyone entering the contests with their entries from previous contests, especially since the subject matter for each contest changes pretty drastically. This is not allowed, and we mention this in our contest rules listed in the main post of every contest (#4: Entries from a previous contest cannot be recycled.)
If you do feel that someone is recycling their contest entries, please PM that information to myself and @Gordon so that we can investigate further. And do not be afraid to enter the contests. The only way to improve is to start getting your entries out there!