Hi James,
When you upgrade a ZD a copy of the previous version configuration should have been saved. You should be able to downgrade back to the exact same version of code you were running before the last upgrade, ie 9.13. If you need to go back any further (9.12.2) the ZD will get factory defaulted when downgraded and you would have to restore a configuration backup taken before upgrade.
When you upload the previous version of code it will let you know if you can gracefully downgrade (ie previous configuration exists) or if the ZD will be factory defaulted, with the option to cancel the upgrade.
Hope this helps,
Thanks for choosing Ruckus Networks.
Albert