I had the same "In Service Date" issue when we had our Sprinter. It wasn't in the M-B database, and had over 500 miles on the odometer, so they couldn't work on it. I ended up seeing the M-B dealership Service Manager who had me sign a form putting it "In Service" as of that date. It was the same M-B form that they would have used if they had sold me the unit...
2022 R-Pod RP-192
2021 F-150 4X2 SuperCrew Lariat 502A, 3.5L Powerboost Hybrid, 3.55 gears, 7.2KW Pro Power, 1,840# Cargo, 7,000# Tow
It is better to have too much truck than to have too much trailer.