Please see below for the area called The Debateable Land. hey were the small orange coloured section at the extreme west of the border. The white line is the Scotch Dyke separating that part of the Debateable Land which ended up Scottish from that which ended English in 1552. Apart from that the border was pretty much as it is since the 11thC. In my side of the country the Tweed/Cheviot line became the border in about 1018 after the Battle of Carham. The only change is really the extreme east where the former Scottish town of Berwick finally became accepted as English in 1482. Apart from that the border never really changed since the 11thC. Scottish kings held land in Cumbria and Northumberland (and even further south) but they held these lands with the English monarch as feudal superior for the English lands. Scotland often tried to annex the northern English counties and push the border south but they finally agreed on the current border, virtually as it is apart from the shaded areas, in treaty in 1237. After that bits of territory at times were occupied by one or the other but it was always regarded as occupied territory not as belonging to the other country.


https://upload.wikimedia.org/wikipedia/commons/9/90/Anglo-Scottish.border.history.jpg