Does a current KMS need old versions' keys?

Solution 1:

For Windows KMS the newer key will activate down-level clients. See section 1.2 Plan for Key Management Services activation for a nice table. The product key group "Volume license for Windows Server 2012 R2" can activate the following versions:

• Windows Server 2012 R2 (all editions)
• Windows 8.1 Enterprise
• Windows 8.1 Pro
• Windows Server 2012 (all editions)
• Windows 8 Professional
• Windows 8 Enterprise
• Windows 2008 (all editions)
• Windows 2008 R2 (all editions)
• Windows 7 Professional
• Windows 7 Enterprise
• Windows Vista Business
• Windows Vista Enterprise

The same is not true for Office KMS. You must install both Office 2010 and 2013 KMS Host License Packs on the same KMS server. Please see How to setup and install an Office 2010 and 2013 KMS Host