If you're using Unity Teams Advanced, we do not delete any version history for your projects.
If you're using Unity Teams Basic, data stored in cloud storage is kept for at least 1 year. Unity reserves the right to delete project history older than 1 year.
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. 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.