How do you know SCHWENPOLIS is the original author? UNDEADNIGHTMARE is definitely not, since it's his only track, and I doubt that he hasn't stole it.
Not having checkpoints doesn't prove it's real. He could have also removed the checkpoints from the original track. But it's possible that he's the original creator.
I noticed that the first two do not have checkpoints, while the last two have. I think, this is a nice plagiarism tree. (One person copies another's track.)
Also, i found another set of copies! http://www.freeriderhd.com/t/6083-3d-city-jumps http://www.freeriderhd.com/t/2529-3d-city-jumps
more copies http://www.freeriderhd.com/t/1166-downtown-halfpipe http://www.freeriderhd.com/t/5977-downtown-halfpipe
MORE?!? http://www.freeriderhd.com/t/10024-canvas-rider http://www.freeriderhd.com/t/6625-hyper-speed
Look, i found a particular author that seems to have most of his tracks as stolen ones: hyjack. Copies of his: http://www.freeriderhd.com/t/5690-monsters and http://www.freeriderhd.com/t/1085-monsters http://www.freeriderhd.com/t/5970-epic-cliffs and http://www.freeriderhd.com/t/4359-cliff-riding
I don't believe it's stolen, just unable to be completed. Gongo999 is one of the top 10 classic authors.
I think I have a way to identify which one is the copies.But to prove if it works,I need to ask one question: Do the numbers at the end (http://www.freeriderhd.com/t/7974-flix) have anything to do with the time it was released?