Range Displayed
The range displayed is not wholly based on the battery capacity and the mileage advertised.
An algorithm within the car looks at existing battery capacity and driving history, examining previous journeys miles per kwh for example and derives an estimate of what range may be available.
Speed, cabin heating, terrain, regen use, weather conditions, to name some of the factors involved, will have an impact on miles per kwh and therefore it is purely an estimate, as was the range when you collected your vehicle.
The range available will not take into consideration the type of journey you may have planned based on the above factors and therefore regard it as just an estimate.