Actualy I think that messages are only kept until all registrered devices (at reception time) get them. For instance if you register a new device to iCloud you

Actualy I think that messages are only kept until all registrered devices (at reception time) get them. For instance if you register a new device to iCloud you never get previous messages (otherwise San Bernadino case is moot cause they could have access this history). I think there is also an expiration time limit running from the moment the first device receive a message for the others devices to get the same message, but we are in undocumented territory about that AFAIK...