I have noticed that if you have never assigned a value to a device's DeviceCheck bits, the http query for that will return a status other than 200 with the message " Failed to find bit state ".
As long as you don't set it anything, it will always return the same message. And once you set it, there is no way back and it will always return bit states with a timestamp and never the Failed to find bit state message.
Is it safe to assume that we can use this as an additional special state? And Apple won't change this in the future (because it is not documented)?
For example 4 bit-states for returning users and one no state for the first-time users.