Neil, There are two different rim letterings but they are on only the CC mint marked pair. The "Ruth Curtis Indpls is the short variety and the other one has a date of 1996 included in it. I have never heard which one came first or which one is harder to come by. It is a variety so alot of collectors don't go after them all but so sure do so if you were to list any on ebay or Jackpot make sure you describe the difference. Could get more bids. There is also one of these of which I forget which one that is doubble stamped and it does bring a much higher premium.

Hope this helps, Dennis