We've observed a steady decline in the number of responses to APNS requests coming back with the "Unregistered" reason. Since about the beginning of 2022, we've noticed that "Unregistered" responses have dropped off altogether for the oldest device tokens recorded in our backend.
Going by the APNS response status, it would appear we're still successfully sending messages to these very old device tokens, but this seems counter intuitive. We would expect the opposite, that over time those oldest device tokens would be the ones most likely to no longer be active (i.e. app uninstalled, devices no longer in use, etc.). Many of these devices tokens were recorded years ago, so we find it hard to believe that none of them would be inactive now.
Does APNS stop providing meaningful response status for device tokens at some point? For example, if the device is no longer reachable (not working, never powered on or connected, etc.), would a request to send a message to that device still have a "Success" response? And if so, is there any way to determine if those device tokens are truly inactive or not?