I have one and have seen a few others. I've never heard of any with carved stocks. I'm guessing it was done after it left the factory. Unless the carving is of exceptional quality it probably doesn't add (may very well detract) any value if the stock isn't factory.
You will find most of the carved stocks were done after the gun was purchased, either by the owner or by a carver for the owner. As was stated above, in general anything done after market as a personalization lowers the value for collectors.
When you are up to your butt in alligators, it is hard to remember your intent was to drain the swamp. Stay focused!