Northern Trail Outfitters wants to add new records to a data extension while retaining existing...

When importing data into a Marketing Cloud Engagement data extension and the goal is to add new records while retaining existing records, the "Add and update" option should be used. This import type adds new records to the data extension and updates existing records based on the primary key or unique identifier. This ensures that the data extension is kept up-to-date without losing any existing data, making it ideal for maintaining comprehensive and current customer data sets.