How to allow my users to edit their submission?

I need a data dump, sure, but I also need a place where the 'client can come back to their form three weeks later with new information.

You can setup an Autoresponder Email that will automatically be sent to your clients upon form submission. Inside that email, you can add an EDIT LINK that will allow them to edit their submission anytime they see fit.

Complete guide: How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date