How to get a F5 BIG-IP VE Developer Lab License
@MichealRP;
A lab license would not be useful for you in this case. They are sold at current versions so if you were to test say an v11.6 to v13 upgrade, the lab license wouldn't be able to be downgraded.
If I was doing the upgrade test, I would use the new VE production license in a test environment, run the upgrade. Once complete I would call support to release the license from that activated VE serial number so I can perform the upgrade in production. I've never heard of anyone having issues releasing the license from the activated serial and the call took about 5 to 10 minutes in my prior experiences.
The above experience you're referencing could have been lag between the internal license where support release the license but the public validation tool wasn't synced up yet? Not sure, but I do know that you absolutely you can reuse the license on another VE once it's released from the previous instances SN in our license database. It's supported and a common practice for test environments.
As an FYI, not sure how BIG-IQ License Manager (free) would ease this up, but I will write up an article on that feature set soon (using BIG-IQ as a license manager for lab systems) and maybe that would help you?