You could order up whatever combination of drums you wished to. The catalog sets were just suggestions/starting points so a 13/16/20 is just as valid as any other combination. It was simply someone's desire to have a set like that.If that's crud on the surface of the wrap it should clean/polish off. If it's UV damage inside the outer blue tinted layer of wrap then you're probably stuck. There are some drastic methods some people try (wet sanding) with mixed results and the potential for causing further damage.
Thanks, I figured it was ordered this way or someone added it later. I'm really not too concerned about the finish since I paid so little. The floor is in good condition and I'm sure it's worth almost as much as I paid for the whole kit.