Years ago I was told by someone who was the local expert on Model 12's that if the second barrel was original to the gun, the serial numbers would all match; the two barrel, magazine and forearm assemblies and the receiver. If there was no serial number on the second assembly, the gun had been fitted by the factory after it had originally been shipped. It may not have actually been fitted at the factory; it may have been done by an authorized repair facility. Of course, if there was a different serial number on the assembly, it had been put together from two different guns. I have had the first two types, and have seen some of the third. The first, is, of course, the most desirable, the second is pretty desirable, and the third is anybody's guess. First and second instance the second assembly would have been fitted to the receiver, the third could be OK, or they could have buggered up the receiver to make everything fit.
