Unless a better scan causes me to reconsider, I think your coil is genuine (one of the rotary types, not an offset). The true gauge is slightly less than 10 as you have found. I forget the exact number, but someone will soon provide it, no doubt. The catalog rounds off.
A hi-resolution scan is highly desired. But even with a fuzzy image, consider when the halves are cut and paired up. The slant of the cut matches, either front or back ...
Specifically, I think your coil was run through an automatic affixer of some brand, which typically cuts the coil near the perfs and often at a slight diagonal. See near the very end of this thread, the left example of the 2 cent stamps, which is cut very similar to yours: http://goscf.com/t/69080
Many collectors would consider the slanted perf-cutting to be damage, but some see it as evidence of the clerical technology of the times.