The FAQ addresses the fact that it is possible for a DSB FDL File to include more than one record for a particular ISIN.
This is a rare occurrence, but may happen when ESMA/the FCA publish data on FIRDS/FITRS after a set cut-off time and so the DSB may still be having unprocessed data for an ISIN, from the previous day, when a new data is received. This will result in multiple records for the same ISIN being recorded and so it is important for the user community to understand how these records should be handled.
Under these circumstances, the DSB recommends that the user should access the ToTV record with the latest LastModifiedDate, as that would have a complete dataset for that ISIN on that day.
Where there is a duplicate entry, the record with LastModifiedDate is the latest dataset for that ISIN.