For reasons, I have been living as a luddite for the last couple of years, I had an iPhone 4S that I kept on iOS 6. I had to stop updating a large number of my apps due to requirements of having more recent versions of iOS. This includes some paid Apps that went to a freemium model, free with paid IAP. When this first happened I remember reading that those that previously paid for the earlier versions would be grandfathered to get the IAPs for free or at a reduced price. As I was unable to update to the newer versions of these apps I never looked in to this. Now I have upgraded to the iPhone 6S on iOS 9. Now that I am finally able to update these apps, I want to make sure I follow the correct procedure to ensure that I am grandfathered into the IAPs privileges, that I believe I am entitled to.
Does anyone know how Freemium and the IAP purchasing process know that have you paid of a previous version of the App?