The Customer needs to talk with their Microsoft Rep, since the rules of their Licensing changed when VDI came onto the scene.
At one time, the customer could purchase an MAK (Multiple Access Key) License, add it to the Gold image and whenever a Guest session launched, it would automatically be ‘activated’. It worked for Windows 7 and Windows 10 Gold images. The other method is to purchase Tokens and setup a Microsoft License server to issue out Licenses. This technique had to be installed in the Gold image.
Also, if the Windows VM was being launched from a non-Microsoft server, you also had to add a Microsoft VDA (Virtual Desktop access) license. Once again, at one time, Microsoft included the VDA License if you purchased their ‘Advantage’ program (maintenance on Windows or Office).
So it is best that the Customer speak with their Microsoft Rep to get the latest Licensing information.