Hey Char - you'd be able to use an enrichment activity to create a link between the csv and the recipient records, have a look at the documentation HERE. My main thought about your plan here is that ZIP code is usually not a unique identifier - so would it really be a good way of getting an insight ...

Incredibly useful post! I can't believe this isn't outlined in official documentation anywhere.I just used this as the basis of a script to iterate rows and remove from a given list, which has massively streamlined a business process.