Since the gun is over 80 yrs old, it simply probably has an old reblue. There are several reblue clues such as blued trigger, smoothness of corners. Originals have a different blue on the trigger guard, like a different shade. Also, compare my side plate to yours, yours is well defined indicating buffing which effects how it fits the gun. On mine, you can barely tell the joint, which is what you want to see. The screw heads are flat on yours, as are the studs on the opposite side of the gun (the end of the screw). Also, S&W blue is much brighter. The shade on your gun could only be from the original finish being lost or removed.

I can't argue that the gun has patina, but you have to look deeper than that. Patina can develop on any gun, original or not. Also, since it was a civilian production gun, you can't compare the finish to a wartime pistol (not that you meant that, just sayin), where quality finish was not a consideration, only durability was. Once you see enough original ones, it will become obvious to you.