Kit406, you’re right, sub-fields are stored a bit differently. I can’t remember how (off the top of my head). I would have to analyze the post_meta table searching for those sub-fields in order to figure out what the difference might be. I’m sure it’s doable.
I wrote this tutorial that you might find helpful. It shows you how to update an ACF field name without losing its data.
https://wpforthewin.com/update-acf-field-name-without-losing-data/