Rob,
Mirror imaging of Ms 12 Camo is not the desired way. It just is that many times photos of a given ship is NOT available for both sides. It is a close approximation to mirror image for some ships. Here are two images of Lardner (DD-487) one of the Federal built Gleaves units that went to the Pacific. The two images were taken two months apart ... at delivery (Federal seemed to take delivery photos of their ships from the starboard side only ... why I don't know?) and after the New York Navy Yard completed her. They show the port and starboard sides, although not exact, both sides followed a "general" pattern. If you look at the photos of other Federal built Gleaves units built in this "block" ... DD-483 to DD-490 ... Federal did not apply the same style of Ms 12 patterns on all ships. One ship maybe similar to another, but they are not exact. The tricky part is figuring out paterns around the stacks and superstructure.
I'm not a Camo expert. But I don't think anyone will ding you for not having the "RIGHT" pattern on the missing side. These two images show that not being exact may be the most correct. Also, notice how the sun effects the contrast of this camo scheme.
Something else I wanted to illustrate. The third image is of Duncan (DD-485) that I scanned at NHHC dated 7 October 1942. This is why I doubt many ships were still painted in Ms 12 at the time of the November 1942 battles.