This How-To covers the upgrade process required to generate the Virtual Essential Edition License when upgrading an from below Release 8.0.
1: Apply Upgrade License
Apply a valid upgrade license for the version that you want to go to, e.g. R9.1 Upgrade License
2: Upgrade the system to Release 7.0
If your system is running at Release 6 or below, upgrade to the last build of Release 7.0: 7.0 (36). If you are already running an earlier build of Release 7.0, then you must upgrade to 7.0(36) as well.
3: Upgrade the system to Release 8.0
Once the system is running Release 7.0(36), upgrade the system to the last build of Release 8.0: 8.0(66).
4: Upgrade the system to your Licensed Release
Depending on what version you want to end up on, you may need additional steps after 8.0(66) to get there.
This should now show the system as having a Virtual Essential Edition License. Please note that this license will not show in offline configs and will likely display an error.
If the license did not generate, an Essential Edition License will need to be purchased.
Please note, should the chassis fail at any point in the future and you need to migrate to a new chassis, an Essential Edition License will need to be purchased as this license is tied to the chassis.