That is bizarre, it does look like it has been used, but that is just plain weird. I would also run it , I think it should work okay. I really don't think it will slip, but it might not shift very well.
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1 Super Record bike, 1 Nuovo Record bike, 1 Pista, 1 Road, 1 Cyclocross/Allrounder, 1 MTB, 1 Touring, 1 Fixed gear