YGO Legendary Duelists: Season 1 - Rules of Play says:

Experience the Legendary Duelists series from the beginning in Legendary Duelists: Season 1! For the first time in almost 3 years, the vault has reopened and beloved, hard-to-find cards from Legendary Duelists and Legendary Duelists: Ancient Millennium have emerged! More than a simple collection, Legendary Duelists: Season 1 remasters the first two Legendary Duelists sets to give Duelists more of what they loved about both.