There is some variation in them mainly in colours and sometimes eye positioning, etc. There are threads with Breyer's comparison pictures of the glitter versions of the main 6 and there is a thread with the differing Pinkie Pies floating around the Corral. Unfortunately there is some cross over between waves and individual releases due to them sometimes being manufactured at the same time. So, yes, almost every release is slightly different [some significant, most minor] however on some of them its almost hard to say for 100% certainty [in case it crossed over in time/wave].