Hi, I did some work on RFC 2317-based delegation in the course of the development of NetBox DNS <https://github.com/sys4/netbox-plugin-dns> which supports RFC 2317 delegation. Yes, the RFC is essentially correct, and using a / in a label is not forbidden either. You can do that, which doesn't mean that you should :-) Citing from https://datatracker.ietf.org/doc/html/rfc2317#section-4:
The examples here use "/" because it was felt to be more visible and pedantic reviewers felt that the 'these are not hostnames' argument needed to be repeated. We advise you not to be so pedantic, and to not precisely copy the above examples, e.g. substitute a more conservative character, such as hyphen, for "/".
In fact an RFC 2317 reverse zone is nothing but a normal zone and does not need to follow the normal delegation scheme for .in-addr.arpa. You can even insert your PTR records in your forward zone, as long as you poing the CNAMEs in the parent zone at the right target. Best regards, Pete.