...
Service Providers are strongly encouraged to support all of the specified alternatives for the shared user identifier and person name attributes described in Section 5 to maximize interoperability. Failure to do so will result in problems even when working exclusively with Identity Providers that claim support for the category. In the case of the eduPersonTargetedID attribute, this recommendation includes the ability to support the SAML 2.0 's "persistent" NameID, which is the recommended modern expression of the eduPersonTargetedID attribute in SAML 2.0.
In accordance with the requirements in Section 7, if an Identity Provider exhibits the R&S entity attribute in its metadata and no accompanying eduPersonTargetedID attribute is recievedreceived, then Service Providers can rely on the non-reassignment of eduPersonPrincipalName values it receives from that Identity Provider.
...
An Identity Provider that does not release all of the required elements of the R&S attribute bundle (shared user identifier, person name, email address), for any reason, SHALL NOT exhibit the R&S entity attribute in its metadata. Exceptions , limiting that limit the release of attributes to specific R&S Service Providers , may be permitted in the event of a security incident or other isolated circumstances.
...