Can I just re-assert something: It's not stealing if they leave the credit (something as little as a sign that mentions you as the original author.) Examples such as PowerShroomsAttacks bridge are not stolen, you should state that you don't want any bit of it copying if that's the case.
How can you check history of saves? Besides looking at the differences between peoples works. Also, you didn't complain when naruto posted that on your thread.