I came here to tell you the answer, but it seems Megaman.EXE have done it already.
Top RIght Corner > PC Info ... Look at the bottom of opened window and check the "Activation Details". If there is no "Activation valid Till xx-xx-xxxx" line, its activated permanently.
You can also add a Microsoft Account this way, and download anything from Store. It also passes the Geniune Validation of Microsoft because the key used to activate the OS is provided by Microsoft itself.