Hey, @AHucks 
This article goes into detail about how this works — Understand pre-populated form fields.
I think this is the most relevant part to what you are asking: “When a visitor arrives at a HubSpot form, HubSpot checks the visitor’s browser for tracking cookies. If this cookie is associated with a contact, HubSpot will be able to pre-populate fields that have been previously submitted on that device,” and "HubSpot will only pre-populate data previously submitted to a HubSpot form on the same device”
I hope this helps get you moving forward! — Jaycee