Headcanon on the Yu-Gi-Oh! series that may as well be canon: the first three shows (OG, GX and 5Ds) are all set in the same universe while all the preceeding shows from
Yu-Gi-Oh! Series synopsis from the official Yu-Gi-Oh! Site.
Theory: The Complete Yu-Gi-Oh! Anime & Manga Timeline - YouTube
Yu-Gi-Oh: A Series History (Live at Japanizam 2017 - subbed) - YouTube