> To handle such ultra long-range flights, Airbus describes the aircraft as being equipped with an extra rear center fuel tank capable of carrying 20,900 liters (5,521 gallons). That extends the aircraft range by 1,000 nautical miles to ensure it can cover the nearly 10,000 nautical miles for the nonstop flights between Sydney and either London or New York.
How did they bridge the gap of 2460 nautical miles?
I am guessing that a test with minimal self loading cargo will need to go further. With <some tons> more cargo it will go <predictably shorter distance>
Or in other words, it went further than the rating because it was unloaded.
Just a guess, mostly to provoke the real aerospace engineers into commenting.