Because by rejecting work from people who've seen the leaked code, you can be sure that your project doesn't become a derived work. That doesn't imply the rever

Because by rejecting work from people who've seen the leaked code, you can be sure that your project doesn't become a derived work. That doesn't imply the reverse; that if you accept code from people who've looked, your project must be derived a work. All cows are animals, but not all animals are cows.