(4)To link the security-by-security data collected from different sources and to avoid duplicate records, all securities that are transmitted to the CSDB should be identified uniquely by an International Securities Identification Number (ISIN code).To ensure the correct grouping of the input data provided by NCBs and accurate linking of the CSDB data with other ESCB statistical information, NCBs should provide, as part of their input reference data on issuers, at least one linking entity identifier that is included in the Register of Institutions and Affiliates Database (RIAD). Furthermore, to facilitate the correct grouping of issuer reference data from different sources and accurate linking with other ESCB statistical information, a Legal Entity Identifier (LEI) should be provided when available.