Hello,
Thank you for posting in Microsoft Community forum.
Based on the description, I understand your question is related to Downgrade Rights in Windows Server 2025 Standard to Windows Server 2016 Standard.
As this is related to license downgrade and license benefits issue, it is recommended to contact your license supplier or Microsoft volume licensing center directly. They will have more access to check your license details and Downgrade Rights.
Here is the VLSC contact info:
Volume Licensing Support Info. | Microsoft Learn
Have a nice day.
Best Regards,
Molly