Not sure about Scotland, but in England you need the deeds to definitively define the boundary. What you see on the land registry map is just an interpretation based on available data. They do not actually know precisely where the boundary is located.
Do they not have their own copies of the deeds? In the states, the local county recorder has all of that deed data on file, and when property is transferred a surveyor is engaged to confirm ground truth matches what the recorder states.
