Wouldn't it be better to use "Edge Slide" for the thigh panel shape after having it aligned, since this panel isn't orientated vertically to your camera's view axis and therefore gets a new orientation different from the local coordinate system by moving the vertices in the view plane?
Ah I see what you mean. Edge slide would be a better option for maintaining the flat plane that I started with. As you point out, the camera angle doesn't necessarily align perfectly with the plane's normal causing my movements of the verts to be non-planar.
Therefore it's certainly valid to use edge slide. But ultimately since I knew the thigh wasn't a flat plane, I opted to move around verts more freely for this blockout stage.