You can’t apply a license on top of a 2012/2016 Evaluation as is – you will receive a “Server 2016 Edition cannot be upgraded” message when putting the new key.
List current edition
dism /online /Get-CurrentEdition
In order to apply the key for Standard, you will need to run this DISM command:
dism /online /set-edition:ServerStandard /productkey:<yourkey> /accepteula
For Datacenter:
dism /online /set-edition:ServerDatacenter /productkey:<yourkey> /accepteula