brskeoch
.32-20 serial number 131452 shipped in April 1930.
.32-20 serial number 132446 shipped in August 1927.
.32-20 serial number 136670 shipped in June 1927.
.32-20 serial number 137511 shipped in December, 1926.
Obviously, they did not ship in serial order. Most likely all four of the units listed above were assembled in the mid-1920s.
Without a records search (for a letter of authenticity from the S&W Historical Foundation) it isn't possible to know exactly when your customer's revolver left the factory.