I acquired what I thought was a 357 Highway Patrolman model 28. Ser num s275xxx for my birthday. I think 1966 or 7? On further inspection, my friend told me that I had a "mistake" gun in that it was originally stamped a model 27, then overstamped to show 28. I can't find any other talk about this. Is this rare or not, and what is the value?