It could be very messy and you could be very popular along with the block 10 down.
The way I see it is that if the boundary is wrong with his opposite neighbor, he'd need to take it up with him. My neighbor I'm disputing with is a rental, and it's up for sale. I'm told that if I formally advise him of the dispute, he has to tell any potential buyer about the problem which won't help him sell the property at all !!