When you first start playing Disney Dreamlight Valley through Xbox Game Pass, your account automatically receives the 8,000 Moonstones that come with access to the Base Edition of the game.
If you later decide to purchase the Base Game after having already played through Game Pass, you will not receive an additional 8,000 Moonstones.
This is because your account has already received the Moonstones once — when your Game Pass access began. Purchasing the game afterward only grants you permanent ownership of the title, not duplicate edition rewards.