Adding new data to existing database

I am adding a new auxiliary field to my current database. So i followed the procedure mentioned Importing data into aux fields in the knowledge base. It uses hybrid mode to combine existing database with new data. Things work fine , if dates match between existing database and new dataset. But the problem is it also adds the dates which are not existing in current database. I only want to add the new dataset for dates which are already there in my existing database, i don't want to add new dates to my existing database. I have used $HYBRID 1$ALLOWNEG 1 to do import data. @Tomasz please guide on how to add new datafields only to existing dates without adding new dates.