I hear you! Was messing about with the firmware update call and one of the firmware release types was "candidate", which I'm not really clear about.
They definitely need to tell us all the possible return values for a call and what they mean.
I believe for the device status call online and offline are the only two possibilites.
I was able to find this for you:
https://documentation.meraki.com/MX/Monitoring_and_Reporting/Appliance_Status/MX_Uplink_Settings
If you look at the Uplink Status section you should be able to find the possible states. I completely agree with you though!