This isn't something I've missed, but something a LOT of toy galleries miss. Cybertron Leader Class Optimus Prime's chest windows folding out all the way to the sides of the fire truck to become side windows in vehicle mode. I can't tell you how many images of this toy online just leave the chest windows in their robot mode position for vehicle mode, leaving the shoulder joints for robot mode fully exposed when they should be hidden behind the windows.
Likewise, an undocumented feature of Animated Rodimus's spoiler not being fully transformed for robot mode. Lots of people leave it where the instructions say, but the instructions in this case are wrong, as they neglect to mention the final steps that see the spoiler's tip unpeg from the piece it's attached to, rotate around 180 degrees, and then be folded down to sit behind the robot mode's shoulders instead of behind the head