I agree with s&wchad, those numbers appear to be restamped for whatever reason.
The s/n will appear on the gun in other places, but the prefix may not be on those other places.
You can look at the inside of the right grip panel to see what is stamped there (assuming the grips are original). Also, push the extractor star all the way out, as if you are ejecting spent shells, and look at the underside surface of the star, there should be a number there.
The problem with these later guns is that they may have the prefix imbedded within the s/n (example 5D12345), is that in the places - other than the butt - you may see these number show us as 512345, especially the grips, they normally didn't stamp the alpha letter, either as a prefix or imbedded number.
The older the gun, the possiblity exists for the s/n to appear in more places, for instance on the underside of the barrel (the flat area that is covered from view if the cylinder is closed, swing out the cylinder and look there, I doubt this gun has it there, it appears too late), also check the crane, on the surface that faces the cylinder, you may need to look through the cylinder with a flashlight to see it, or dissassembly may be required.
Good luck