I had a meeting with Volkswagen engineers from Wolfsburg yesterday and it's all much clearer now. The reason for the delays and some of the problems last year was the development process of the software for something like 1000 different engine, transmission and vehicle combinations. 250,000 kilometres were driven to get test parameters for 1000 vehicles then in developing the software a further 8,000,000 kilometres were driven and final approval of the last software update was not received from the German KBA until 13th December 2016. With the new software the engine has to produce the same power and torque as before with the same fuel economy and the same CO2 emissions. Reducing the NOx emissions means increasing the soot emissions which means the DPF and/or SCR system has to work harder, using more fuel. But using today's technology rather than the technology of ten years ago it has been possible to improve the fuel economy of the engines sufficiently to cover the fuel used by the DPF. The answer is, from what I gathered, it is now okay to get the software fix.