Downgrade rights allow users to purchase the latest version of a particular software licensing, and use it with previous versions of that same software. This is typically done when an older system is currently being used, with plans to upgrade that system at a later time to the newer version.
If you have OLP licensing, you are given downgrade rights and transfer rights. Transfer rights would allow you to use previous Windows Server versions until you are ready to migrate to the new version. Once you’re ready to upgrade, uninstall the older version and install the newer version while also remaining compliant.