Trying to pin down a date on a H&R 38S&W

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I've been trying to narrow down a date for a Harrington & Richardson Top Break 38S&W.

What I know. It seems to be on a version of the heavy Sportsman frame with the dual trigger system, 4" barrel, 5 round cylinder, nylon grips, no finger rest trigger guard and the only markings on the barrel are Manufacturer name and address & Patents on the top strap and cartridge designation on the left side. There is no model number, model name, date letter in serial number or other identifying marks. The serial number is on the front grip strap, under the grip and on the cylinder face.

I have a 1940 brouchure where the gun is shown as the "New Defender" but it shows the name on the barrel.

The serial number is really, really low (#234) and as I said, there is no date code associated with the serial number. The blueing is fantastic, deep and luscious.

The sights (loosely called sights) are fixed and non-adjustable. It is auto eject. Lockup both frame and cylinder is tight. The cylinder is the early lift and turn to remove system.

I have found later versions of the gun called the Model 25 and even 925.

My current guess is that it is an early model made between 1935 and 1939 but I'd love to find keys that might pin down a closer range of dates.