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Yours is early as they only have the cocking indicator buttons for the first two years or so.

The NID came with cocking indicators thru 1934. The earliest NID Field Grades just had the roll stamp on the sides of the frame.

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[Linked Image from i.imgur.com]

By 1927 the folks in the factory were adding the stars to the frame --

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but the folks in the office didn't add them to the catalog picture until 1929.

For 1935 they dropped the cocking indicators, much improved the stock and went to some border engraving around the frame and some stippled panels on the top of the standing breech for the Field Grade.

[Linked Image from i.imgur.com]

After WW-II some Field Grades had no engraving at all on the frames --

[Linked Image from i.imgur.com]

and a much smaller patch of grip checkering.