I think this is the key quote:
"In short, the belief is usually that the design studio has precedence, and everything else isn’t canon. That’s actually wrong, but several aspects reinforce the misjudgement, not least that a few top brass quotes have been poorly phrased or taken out of context; some novelists wildly diverging from the source material for reasons apparent to no one but themselves; and the fact that the design studio has 30 years of history where it was essentially the sole source of canon. Its products are the foundation for the whole license – it’s the source, the core, the chewy nougat centre at the heart of it all. With the weight of history and its place as by far the most widespread, its published lore reaches the most eyes and ears."