Thank you. I deeply appreciate the info. I'm now thinking I need to carefully try to do a more detailed inspection and find out why my Model 15-4 does not show a serial number, except for the X7XXx on the yoke. I have 2 theories: 1) the X7XXx on the yoke is not the S/N but some other assembly number (S&W says the only S/Ns that were placed on the yoke were those models that were factory shipped with target grips--mine does not have target grips, so possibly they were removed at some point), and 2) the 15-4 S/N must be somewhere else or it has been removed from the butt--but the finish looks perfect. Oh well, the search continues--thank you again.