RFC 7484, "Finding the Authoritative Registration Data (RDAP) Service", March 2015Source of RFC: weirds (app)
Errata ID: 5460
Reported By: Pieter Vandepitte
Date Reported: 2018-08-14
Section 8 says:
In the case of a domain object, the client may first query the DNS to see if the respective entry has been delegated or if it is mistyped information by the user. The DNS query could be to fetch the NS records for the TLD domain. If the DNS answer is negative, then there is no need to fetch the new version of the registry. However, if the DNS answer is positive, this may mean that the currently cached registry is no longer current. The client could then fetch the registry, parse, and then do the normal matching as specified above. This method may not work for all types of RDAP objects.
I would remove the whole section. The point is: if the DNS answer is positive, then you need to fetch the registry. But if the answer is negative, this does not mean anything because it it possible that a registered domain is not delegated.