I have searched and searched but it is not entirely clear, I haven't programmed much in years, I have to update an old app for a client that will be using iPods iOS 6 and new iPhones with iOS 9 logged into the same iCloud account.
Will changes to core data of app on an iOS 6 device update content for the iOS 9 device?
I have not experienced problems with updates to iCloud in NSSUserDefaults when testing on iOS 6 and ios9 devices (with iCloud drive disabled)
I cannot get iCloud for core data to work on ios9 iCloud drive disabled, so I need to update to iCloud Drive... But I am worried about data on other devices not updated. Debugging nightmare?
Core Data with iCloud is really flaky, I really don't recommend it.
Devices that have switched to iCloud Drive will make changes that won't be visible to those that haven't (including those devices that don't support it, most definitely those running iOS 6). Not sure about the opposite, but it's probably the case as well.