The novelizations of Episodes I-VI and the Clone Wars movie are considered Canon where they align with the films, as explained by Del Rey. Because they were written well before 2014, any extra scenes are not considered Canon until canonized elsewhere.
The same applies to the recent film adaptations as well. While the Lucasfilm Story Group is involved in their creation, they are still considered Canon only where they align with the films. However, their involvement and the fact that the novelizations (now dubbed as Expanded Editions) starting with Solo: A Star Wars Story have come out months after the movie means that the stories tend to fit better with established Canon.