It is possible for no one to have possession of an item, which is a major distinction from ownership. If a bike is left alone in an open field then no one has possession of it until someone comes and takes it i.e. exerts their care and control over it.

My gut tells me that if a key were split into several parts, each of which was unstable on its own, then the holders of those parts are not in possession of the key.

If you have the pin but not the wallet itself, I don't see how you could be found to have possession as you cannot actually move funds around (no care and control). Having the pin may be an indicator of ownership however, as we will look at next post.