Smith & Wesson has had a few little slipups with the model and caliber stamps, too. They don't seem to bring high prices like mismarked stamps and coins. I don't doubt your FiL has such a gun, but it was not a catalog item, it was a foulup at the plant.
(They did a good many Model 25s marked Model of 1950 instead of 1955 before somebody noticed what was wrong.)
Now if it has a 7 3/8" barrel that IS odd. Or did you mean 8 3/8" which is fairly common.