Export data from case registration and follow-up forms together

I'm using Commcare for a longitudinal study. I created cases via Excel import that has identifying information for each case and used an External ID number. However, when I now want to export the data from my questionnaire (which is a follow-up form), I can't figure out how to link my external ID to the follow-up form data when I export it. How can I export the identifying information from the case registration with the follow-up form data. It is critical that the unique identifier in the case registration export along with the questionnaire (follow-up form) data.

Thank you,

Does the form operate on that case? If so, you can make a hidden value in the follow-up form where the calculate condition references the case's external ID. This will save that ID to the form.

Thanks, I've just added it as a default value (hidden value) since it was a case property. I assume it will not appear on the 300 forms already completed? Any suggestions on how to handle those forms?

That's correct, it won't appear for already-completed forms. I don't think there's a great way to fix that unfortunately - forms are a mostly-static record, whereas cases are longitudinal records that are modified over time. If you were looking at a case export, you could make edits to that using the case importer, but there's not an equivalent for forms.

Ok, thank you. Bummer. I completely misunderstood the case registration and follow-up forms relationship.