Let's say an MN-CSE announces an areaNwkInfo to an IN-CSE. The areaNwkInfoAnnc resource in the IN-CSE has a listOfDevices attribute that contains a list of MN-CSE-relative resourceIDs.
Is that correct? If so, what use are those resourceIDs in the IN-CSE? How, for example would one map those resourceIDs to announced areaNwkDeviceInfoAnncs ?
No, that's not correct. The MN-CSE (as originator of the announced resource request) should set any resource identifier reference to the correct format (as per TS-0001 clause 7.2, latest paragraphs). In your case, SP-relative.
In addition, if I am not wrong, areaNwkInfo resource cannot be announced as per TS-0001 Annex D.5, table D.5-2.