When installing the Volume Activation role on Windows Server 2012 R2 and activating it with a Server 2012 Std/Datacenter KMS host key, would I still need to install the older product versions' keys (Server 2008 - Server 2012) to get the Vista+ and Server 2008+ instances activated?
The same question goes for Office 2013 - will an Office Pro Plus 2013 key activate Office Pro Plus 2010 as well?
Our "old" Server 2008R2-based KMS server which is due to be phased out is listing a plethora of keys as the output of slmgr.vbs /dlv /all, most of them with License Status: Unlicensed, but I simply do not know if this means they are never ever used again.
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:
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