My guess (as a former Customs Officer) is that it may be a port rotation number or other sequential number relating to the Port of Tyne or perhaps a Volkswagen code, 717th shipping movement to Tyne, something of that nature. To be honest I'd never given it much thought.
Bear in mind that the screenshot I posted is from a Volkswagen UK tracking screen which my salesman may nor have been supposed to show me, but I did get screenshots at three points during the progression of the order.