GeneXus licenses, though granted for a specific GeneXus version, can be used in prior GeneXus versions.
When authorizing a GeneXus version, you are able to use previous versions without the need to authorize or transfer the licenses between them.
So, when you get a GeneXus 17 license, you can use that with GeneXus 16, or even prior versions, as GeneXus 6.1.
However, in certain versions, you need to install some compatible upgrades, as follows:
Note: If you use centralized licenses (installed in a server), you will have to install a GeneXus Protection Server that can hold license keys for the latest version of GeneXus. Supported GeneXus versions are listed here: GeneXus Protection Server