To understand canon and continuity, the overall Star Wars saga should be looked at as a set of stories written by many different people which «document» past «events.» Although some stories are more reliable than others, they all are looked upon as part of the overall «history.» It should also be remembered that all of these stories are simply that—stories. There are numerous errors that inevitably arise between the stories simply because different authors have their own ways of telling the story and may not have the time and resources to perfectly align the details. This site deals with non-canon material by putting red text notification above the non-canon items.
The situation can be compared to Greek and Roman mythology, or the stories of King Arthur. The various Star Wars tales are a group of separate but linked stories, and are told by many different authors over a period of time.
As of April 25, 2014, the only previously published materials that are considered canon are the six Star Wars films, the Star Wars: The Clone Wars television series and film, novels (where they align with what is seen on screen), and Part I of the short story Blade Squadron. Meanwhile, the Expanded Universe is no longer considered canon and was re-termed as the «Legends» brand. Most Star Wars material released after April 25, 2014—with some exceptions—is composed in collaboration with the Lucasfilm Story Group, making it part of the «new canon.»