The official performance targets provided by sales and marketing are riddled with data traps. Even saw one (not Airbus) providing result sheet for a customer-specified mission where ZFW was used for cruise burn calculation.
The AFM data, on the other hand, are dead accurate. Take a brand-new piece from the factory, or a 16 year one from storage with worn engines (adjusted for perf. factor), and the airplane delivers exactly that. Assuming your atmo model for planning is accurate and hell they are (for decades already).