Forum:KB:The Ahsoka Novel

I was listening to the new Ahsoka novel and I feel what happens in the novel contradicts other canon material. In the book when Ahsoka starts helping out the rebels Antilles is clearly already a part of the rebels and seems to be pretty high in the pecking order yet in the tv show rebels Antilles is still a cadet for the the imperial navy long after Ahsoka assumedly dies in the show. How can something be considered canon when it so openly contradicts the other canon material?