Tag	Field Name	Data Type	Description	Used in
523	PartySubID AbbrName: ID	String	Sub-identifier (e.g. Clearing Account for PartyRole (452)=Clearing Firm, Locate ID # for PartyRole=Locate/Lending Firm, etc). Not required when using PartyID (448), PartyIDSource (447), and PartyRole.	PtysSubGrp