It seems to be a fast moving market at the moment. I wouldn't feel too sour about it, Tesla are still doing you a favour here. How much do you think you would get for it selling privately or to a dealer? For our last trade in, Tesla were £8.5k ahead of any other offer I received. Even a private sale would have been nowhere near the Tesla trade-in, with all the hassle of having to deal with tyre kickers. Tesla didn't even look at my car when I handed it over. Easiest trade-in I've ever experienced in all my life!
I wonder if they make minor adjustments based on what car and spec you order against the trade-in? Like if they know your new car is 2 months away they might adjust for the trade-in car to compensate. I don't think the photos make any difference unless there is some glaringly obvious defect.
Or maybe you were just unlucky that their book price got updated.