We have some small similar apps in appstore with small portion of content in each, every app is paid. Now we made large app with in-apps and all content from previous apps + new features and some new content. App is free. Users are asking for getting content from previos apps for free and it's honest - some of them already paid for it
Update: To be a little more specific - I need to choose between 3 ways:
Updating small apps (like said in the first answer) to use keychain
Updaiting small apps to send sone unique codes to our server (or other custom way of detecting)
- Find a way to it without updating small apps (a lot of them!)