Absolutely luck of the draw mate, it totally depends on the availability of the on hand components.
They use a computer system to align the component list of your car with the arrival (note I say *arrival*) of the individual components which come from a variety of different (mainly external) suppliers. When the system predicts the bits will all be there they are allocated to your car's build.
Its called "just in time" or nowdays ERP and its a concept created by Toyota many moons ago to reduce costs in the motor industry but also used by any large scale manufacturer of stuff - my own company included.
Whilst they try to predict demand and match orders of parts from suppliers to predicted demand, demand isn't constant and sometimes you get lucky in ordering either when there is slack or when demand is as predicted. They will have a target for order to build times, but this can be missed for all sorts of reasons (extra unpredicted demand caused by disconnect between marketing and production, economic downturns, sudden weather changes etc).
And absolutely none of this is communicated with dealerships or even VW UK...
Anyway, just a little background from someone in manufacturing
