One of Xanadu's goals was (is?) to uniquely identify documents, which isn't inherently tied to either access control or rights management.
The process and theory of identifying documents is one of the oldest subjects of interest in library science[1], and the Internet is chock full of unique identification schemes (URIs, nominally, but also OIDs, DOIs, ORCIDs, &c.).
I admit my eyes glazed over half way through, but this[1] seems to suggest their "transcopyright" system incorporates permissions and micropayment systems.
Yeah, they've got a whole complicated permissions scheme that, to the best of my knowledge, does not and has never fully existed.
The parts of Xanadu that do exist seem to be mostly "goodfaithware," if you'll excuse the term. It's not clear that they have any real protections (like DRM) against clients copying data and/or not obeying the unique addressing scheme.
The process and theory of identifying documents is one of the oldest subjects of interest in library science[1], and the Internet is chock full of unique identification schemes (URIs, nominally, but also OIDs, DOIs, ORCIDs, &c.).
[1]: https://en.wikipedia.org/wiki/Authority_control