Its a whole new process (that not only took into account the unit prices but also calculated the 'life cycle costs' - which takes into account the cost of maintenance and spares for the period, estimated at 40 years, the aircraft would remain operational) and is the FIRST of its kind in the world, ever! When calculating life-cycle costs for the coming 40 years, aren't certain assumptions bound to be made?? There is no way to be 'precise'. The assumptions were probably made with the 'most likely' predictable use of the aircraft over a number of years based on the information available today. There is no way in hell one can come up with precise numbers without making certain assumptions.
Its like someone asking them to precisely predict the future and even if they come up with most probable scenario, its not good enough.. If its a matter of miscalculation, its understandable but when a finance minister questions officials about cost associated with respect to their assumptions (for example..) of likely flying hours, sorties, fuel consumption for those sorties, service hours, etc over the course of the life of the aircraft, it seems ridiculously unreasonable. I just hope common sense prevails.
Its not the first time in the world. Companies like Boeing and Airbus do such analyses regularly while pitching aircraft for airlines. Boeing especially has some very good analysts who have some good models on airplane performance, lifecycle costs including introductory costs and maintenance costs. From being personally involved in such analyses, I can say that a LOT of assumptions are made because some real world scenarios just cannot be modelled without making a model that becomes extremely complicated.
For instance, how does one know the exact utilization per day (in flight hours) that an airline will make of its fleet for 50 years? They go with a simpler calculation that basically looks at the routes that the airplane will serve, the estimated time for each route, the network efficiency factor for the airline and then come up with the number of flights per day- using that they devise the maintenance schedule for 50 years (when a A, B or C check must happen) to come up with the estimated costs of operating that airplane over 50 years.