My understanding....The "pre" designation means that the model 23 when issued was based on this gun. They didn't start using model #'s until the late 50's??
Could a wise man, given good pictures, determine whether a proofmark was applied and then reblued? I'm thinking that the cylinder locking notches look to be below the blueing.
Under the barrel, genius! That and the cylinder are all # matching. If the cylinder and/or barrel were replacements, they couldn't (?) have the BNP proof marks?