Luna
![Image](http://i.imgur.com/7XfgpCr.jpg)
![Image](http://i.imgur.com/SmXNHY6.jpg)
Alex
![Image](http://i.imgur.com/6MgTFaT.jpg)
![Image](http://i.imgur.com/m0Stgya.png)
The only difference I can see between pre-release and artbook Luna (besides the hair color
![Razz :P](./images/smilies/icon_razz.gif)
Alex, however has quite a few differences with the art in the art book. First off, he has a mullet, while artbook Alex doesn't. His coat is purplish in the pre-release screenshot, while the artbook Alex has a brown coat. Pre-release Alex has a slightly-off-looking smile with his teeth exposed, but artbook Alex has a basic smile. Pre-release Nall's back is purple-blueish, while artbook Nall has the final colors. For some reason, the flaps on pre-release Alex's ushanka are green, but are the same color as the rest of the hat on artbook Alex. Finally, pre-release Alex is tilted slightly right compared to artbook Alex as well.
Basically, my feeling is that the images seen in the artbook are later versions of the art shown in the pre-release screenshots.