Board Thread:News and Announcements/@comment-9346948-20160512213814/@comment-32509213-20161016223910

I think the difference is that The Flash is a spin-off of Arrow, and that Legends is a spin-off of both Arrow and Flash drawng supporting characters from both shows. (Vixen too) They frequently cross over their characters and often reference events that happen in each other’s shows, sometimes to the extent where events in one show can start affecting another (i.e. a couple meta-human villains appearing in Arrow, Laurel's death affecting Sara's activities in LoT ep201, etc). In contrast, Supergirl was not a spin-off of any Arrowverse show and has only a crossover with a single character, Barry Allen, the events of which have never been referenced in The Flash. It doesn't have frequent crossing over of characters (main, supporting, or otherwise) or referencing of events from the other DC-CW shows.