Not quite Scotland, but Northumberland 250….
Recently purchased a book and official map of the route. The book only available while stock is available, and not to be reprinted.
https://northumberland250.com/
Following this heads-up from EVskij in another thread, I ordered a copy of the route and the map from the Northumberland tourist office. I then did my best to cut the route in MyRoute.
https://www.myrouteapp.com/en/social/route/6606723?mode=share
I think the route is near enough correct, coming out at 262 miles. I suggest that the 12 miles difference might be down to nothing more than the tourist office taking a little licence when it comes to naming it.
It is certainly not an area I know at all well, so I can't judge how good or bad it is. No doubt the route does miss some "Must do, mate...." roads but I don't think that is its purpose. Rather, I suspect it is designed to show-off the area's sites and views (they are not short of a castle or two) for tourists and take them down some sometimes quite small roads in doing so.
Anyway, it's a nicely produced map and accompanying book. Hopefully somebody will make use of it.