2012 Sql standard Core license

Hello,

We currently have one sql server(sql server A). 

SQL server A has 8 cores (as per windows server task manager). Our current volume licensing summary says we have 8 quantities of 2012 Sql server standard core. I understand for 8 cores we need 4 quantities of core license. That said if we buy a second server( Sql server B) with same number of 8 cores can we use the remaining 4 core license from the existing volume license  ?

So, we want to know if any existing unused sql standard core license can be used on another new server or the issued license is tied to existing server and for the new server we will need to buy another 4 count of sql core license.

thanks

gans