Mercedes were caught with their trousers down and the German government forced them to remove their emissions defeat software. Here in the UK this took the form of a mandatory recall to apply a software update known as SRPC 1838. Essentially MB programmed their engine control software to meet the exact requirements of the emissions and fuel consumption tests which take place under very controlled conditions and the resultant figures are used to help influence customers to purchase the car. However, they bear no relation to the real world figures. A consequence of the reprogramming in diesel-engined cars caused a significant increase in AdBlue consumption which in turn caused the various engine sensors to report a higher fuel consumption, a increase of 10% being typical in my case. However, I have no evidence to prove the pre-update fuel consumption was correct in the first place. Only by brim-to-brim filling and manually recording the fuel used for the miles travelled both pre and post recall, could I confidently say my fuel consumption has increased.
On a side note, MB were falsifying the emissions and fuel consumption figures back in 2016 when I bought my 220d Sport. There is now a class action in the UK for compensation due to their false claims. I've signed up as a claimant but it is expected to be quite a lengthy process before a Court decision is reached.