For my '15 500 RS The 750ml reccomendation is a safe level to insure no overfill whether changing the filter or not. When the filter is changed, it takes more oil to refill the filter and it's chamber, so the 2 levels are different.
With no filter change, 750/800 seems about right, although I fill mine until the sight glass is covered with the engine idling. With a filter change it takes a full liter, and I run a full liter in the transmission also.