Hold on, if the XC is going to Edinburgh - doesn't that mean that the routing guide has no effect, unless there is a specific easement that states otherwise?
Only if it was a through train from London to Edinburgh, which it isn't.
I had actually noticed this too recently - was looking for good value fares for a friend of mine who needs to travel from Oxford to Edinburgh with the outward journey on Fri 27th, stopping off overnight in Leeds, then returning from Edinburgh on Mon 30th, preferably straight to Oxford (although a stopover in Leeds would be possible if it led to cheaper fares).
I looked at this quite a while ago and there seemed to be no cheap advances going to Edinburgh on the Saturday because the West Coast Main Line is closed somewhere. So I decided a SVR OXF-EDB rte NOT LONDON was the best option - £79.60 with a Y-P railcard and available any time (8X restriction). But more recently I noticed the SSR from London Terminals to Edinburgh undercuts this at £75.65, and via Birmingham takes an 8X restriction so no issues for heading northwards on the Friday evening. But I also came up against the problem that going direct from Birmingham to Derby doesn't seem to be allowed on map AS, which means she couldn't take the mid-afternoon direct train from Oxford to Leeds - which otherwise would have been very handy. Manchester to Leeds direct also seems to be barred from map AS. Very strange.