A Bedford-London Terminals ticket is valid only as far as St Pancras.
London Terminals in the context of tickets includes stations like London Bridge and Waterloo.
So if you take the ticket at face value, can't you use Map LB in the routeing guide to travel on a permitted route to, say, London Bridge (in the London Group, which explicitly allows travel to/via any such stations on the permitted route) and just break your journey at Farringdon Thameslink?
). The TVMs at Bedford all issue 7 day seasons correctly i.e. to London Thameslink - and the renewal of monthly seasons is disabled - I presume for precisely this reason