Adam, thank you for clearing all of that up. It shows that you can observe photos as much as you like but not understand the true meaning of them without other knowledge to back it up. It makes sense that there are often good photos of the prototype that are well preserved, but also often not representative of the rest of the production run.
Interesting about the Kubinka vehicle, it means that it is the same vehicle in the photo below, and it confirms that, for whatever reason, someone decided to rebuild the track guards which were lost at some point, and they also fixed up the side armour...
Matthew