If you're using Unity Teams Advanced, you have access to unlimited history for your projects.
If you're using Unity Teams Basic, you always have access to the latest version of your project, but you only have access to the last 90 days of your version history. Additionally, with Unity Teams Basic, only the last 1 year of your history is stored.
If you're using Unity Teams Basic and want full access to the last 1 year of your history, you must upgrade to Unity Teams Advanced. Once you have upgraded to Unity Teams Advanced, you have access to your full history going forward.
For Unity Teams Basic users, Unity reserves the right to delete project history older than 1 year.