Synology actively maintains a database of legitimate keys. If a generic key is shared widely on the internet (often used by unauthorized sellers), Synology can blacklist that key during a firmware update. When this happens, your cameras will stop recording, and you will be locked out of the system until you purchase legitimate licenses.
Some specialized cameras (like multi-lens panoramic units) might consume more than one license if you want to view each lens as an independent channel . Ways to "Expand" Without Buying Licenses synology surveillance station license free free