Sounds like you did it right. If you changed the app group, then the old data shouldn't be visible, because it is in the old group. If you changed the app group to something you had not used before, the group should initially be empty.
If you're working on an unreleased app this might not be an issue. For apps already in production though, some kind of a migration is probably warranted. I believe colink is discussing this latter scenario in their messages above.
welou
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