Halo 4 Limited Edition UNSC Handbook mistake

I know it is a small detail and I probably should have addressed this earlier, but there is a mistake in the book that is property of Gabriel Thorne. It says that the DMR has a 15 round clip (like inReach) and i believe that it originally did in the earlier stages of Halo 4, but I was just wondering if this was actually on purpose or a mistake? Does anyone have any clarification on this matter?

On a separate note, why is the AR 99.9cm, why couldn’t they just make it 1m/100cm?