in front of each observer is a slime block and if you update the observer at the back it will create a randomness and some pistons might not push , just make it yourself and do what I said and see what happens , if it works for some reason which only halpenned to me once push the back with a piston and it will proboly be random that time but I bet it will be random the first time I put a pictur of what happens but you should try it yourself