From p. 4 of Summary of Programmatic Changes to the LC/NACO Authority File: What LC-PCC RDA Catalogers need to know,
1. Conference headings: any AACR2 authority record with a 111 field, and any authority record with a 110 field containing subfield $b whose text is present in a list of terms that mean "conference" in some fashion, will be labeled with a 667 field indicating that the 11X field must be reviewed before it can be used under RDA.
At Indiana we have noticed a couple of authority records that were flagged with the 667 note “THIS 1XX FIELD CANNOT BE USED UNDER RDA UNTIL THIS RECORD HAS BEEN REVIEWED AND/OR UPDATED” for which we cannot see any obvious reason for the flagging. One example is the AR for United Nations. $b General Assembly (n79007295). Can anyone enlighten me, please?