I have an iOS game with one Game Center leaderboard. I published the game a few months ago and now I'm working on the OSX version. I want to use the same leaderboard for both versions of the game, which means that I need to create a Game Center group. The problem is that Apple forces you to modify your leaderboard ID's when you move them into a group:
Group ids must begin with grp.
Now, if I do that, I will need to update the iOS version of the game so that my users can keep posting their scores, and if I release an update for the iOS version of the game, players who don't install the update will no longer be able to use the leaderboard.
My question is: Is there a way to use the same leaderboard in both versions of the game without having to update the iOS version?
Thanks.
You don't need to update the iOS version. As you guessed already, the old IDs continue to work (under normal circumstances). If you add new leaderboards or achievements, they will be added to the grp.* though (necessitating an update if you want these to be picked up by the iOS version).
The sandboxed grp. leaderboard does not inherit the live scores from the iOS version, the old leaderboard scores for the live iOS version should be still intact.
The live grp. leaderboard should inherit the live scores from the non-group iOS version leaderboard.
In general, sandboxed leaderboards and achievements can get wiped from time to time, and it also takes some time (a couple of hours sometimes) for changes in your iTunes connect configuration to reflect properly in the sandboxed GC database for your app.