My Sprinter calls for Service A at 20K miles. Service B at 40K. Being old school I changed my oil and filter at 10K. My manual has fuel filter as Service B (40K miles) item buts adds or 1 year. Then I have had the fuel filter changed annually at a Sprinter shop in Greenville, SC.
(Discussions on the sprinter forum did not consider the fuel Filter change as a DIY project.)
Fuel filter change also requires removing and replacing a new Turbo Inlet seal.
At 20K miles I had the local MB Sprinter dealer do the complete service A just for the warranty book.
The reset .51 or .31 describes the spec for the oil used. From the Mercedes approved fluids list. Your 2016 manual may call for 226.51 or the newer 226.52 oil
MB 226.51 - Low SPAsh multigrade service engine oils (Specification 226.51) - Mercedes-Benz Specifications for Operating Fluids