I was fairly sure that Approved Used cars required a full MB service history. But there's no mention of service history at all on the MB UK website:
Mercedes-Benz Approved Used combustion, electric, and plug-in hybrid cars. All come with an in-depth technical check & one-year unlimited mileage warranty.
www.mercedes-benz.co.uk
The warranty handbook is downloadable there, and that does state ...
That's obviously while the warranty is in force though.
It's reasonable enough to ask to see the past service history before you purchase it, IMHO. But the warranty is excellent and the car will have had a thorough inspection before sale, so would (for example) a late or non-dealer service at some point in the past be a deal-breaker for you?