I have been to the top of the Bitdefender chain, and here are the accurate answers to the licensing questions:
When a Bitdefender GravityZone license key expires, all the endpoints will enter into 30 day trial mode.
When a Bitdefender GravityZone license key count is exceeded, all the endpoints installed over that limit will enter into 30 day trial mode.
Checking a license key validity is done by multiple communication paths using multiple algorithms. If a communication error appears, a console fails, internet goes down or a license key bug surfaces, the endpoint will enter into 30 day trial mode. This will be reported in the console, allowing the admin ample time if action is required. This issue usually mends itself requiring no intervention.
Please let me know if there is anything I can do to help, and have a great weekend!