That is true, Jarvy, that they are pre-allocated but, as I understand it, they are only allocated just before the online check-in opens and not when booked. I believe some carriers use an automated system to populate the seating plan, based on requests but BA seem to use a manual allocation based on requests. It must be a real jig saw with so many 'special pleadings', families, singles, window/aisle requests, Silver/Gold etc.