Sure in that scenario but I feel that's an edge case scenario. More commonly a machine you use is acquired by an adversary. Thus the machine is expected to have

Sure in that scenario but I feel that's an edge case scenario. More commonly a machine you use is acquired by an adversary. Thus the machine is expected to have a working installed OS on it. If that laptop lacks an un-encrypted partition then the adversary will assume it is encrypted. They don't need to mathematically prove it.