...the order of the towns is known information and the scouting ability on the building is an ongoing thing, as in you know before taking the attack action if you can conquer or not, so the situation you've described wouldn't occur as you would know before hand if the attack would be successful or not.
This is my understanding as well. The order of the towns is public information. Anyone can look at what towns are below the topmost town. However, only someone with scouting is able to conquer a town that is not topmost.