I doubt Airbus data would be wrong. Airlines are hardly going to decide to by $100 millions worth of planes simply based on a few numbers up on the manufacturers website... If the numbers were wrong, I'm sure the airlines would be able to get their money back anyway.
In terms of fliers, they don't really care what the plane's stats are - they are more concerned about airline specific seating and scheduling.
One thing is what they tell the airlines, another is what they post on their website. It's called marketing. In 2005 Airbus claimed that the proposed A340-600E, an improved A340-600 with A350 (the original A350) materials and updated engines etc. would be a 777 killer. Never quite happened. They said the same about the A340-600HGW, and that one hardly sold any frames. And look at Boeing in the KC-X competition, claiming the 767 is far cheaper to operate than an A330 (which it is, but CASM is higher).
