Lets say I have old iOS that is not compatible with GameCenter. I played games and for example got many achievements in these games but not on game center (because I have no game center in my iOS) but in the game's private social network. Now, if I'll upgrade my iOS to 4+ and have a game center, when I'll play the game it will sync the achievements to the game center or they will stay only in the game's private social network and I'll can't unlock them in the Game Center?