I may have stumbled on to something.  Last night while cloud saving / restoring different game instances i noticed after a restore to different device - from iPhone to iPad or iPad1 to iPad2, previously collected achievement GC were reappearing for collection.  I couldn't discern a pattern or whether or not its repeatable but it did happen after just about every restore.  I even tried restoring, clearing and restoring again to the same device with the same cloud save - i did receive 3 or 4 GC.

This isn't a bonanza like the 50 or 200 GC process - largest i saw was 40 GC.  Has anybody else seen this?