I'm pretty sure the OB ones are quarry marks, mostly on account of the profusion of quarried stone lying right next to the carved panel. (You've got to be careful interpreting those old sketches and lithos of RA. You know how people have a tendency to see only what they want to see.) Exactly who did the quarrying at OB etc, and when, is open to debate. Some IA Northumbrian hillforts have revetments made from quarried stone, eg. Yeavering and Humbleton.