Board Thread:General Sly Cooper discussion/@comment-24894472-20160709003821/@comment-1845428-20160709031823

They're canon because they are. There are minor discrepancies and changes in the canon of many universes; it's called a "retcon." Just because something is slightly different doesn't mean it should be wholly disregarded as false. The comics provided us with a lot of important information, such as the introduction of Dimitri and explanation of how Sly knows about Kaine Island. If you want more information about how the canon works, read this.