There is something, I believe called shadow volumes, which are completely metadata less encrypted containers living in a sea of random numbers. While you could claim that the existence of a program able to acess such a volume would be equivalent to metadata, no actual metadata needs to exist, and the random sea could contain one or ten volumes, which without a password you could never know, only guess or assume.

It is could even be possible, even likely, to create encryption schemes where several different encrypted volumes could share the exact same data blocks using something similar to homomorphic encryption. Which raises and obvious question: If the unlocked drive did not contain the data sought, can we hold someone in contempt after they did what we asked from them simply because we didn't find what we were looking for? Because we truly can't know if there is several encrypted volume in the same space without assumptions about information entropy and inaccessible configuration data.

Thankfully homomorphic encryption is not really practically viable today, so that particularly nasty can of worms is not imminent to solve, but we might be well served to let out decisions be informed by it, as it breaks most assumptions of what can be known, and what can't.