The early patent and the small underlined 6 date code means you can be confident about the 1926 date (as per John Loring's invaluable
The Dunhill Briar Pipe/The Patent Years and After). To go a bit further down the relevant rabbit holes, yours is a Bruyère finish (as opposed to a "Dead Root Bruyère")--which most Dunhills of that time would have been.
As for Dunhill pipes of their earliest period--I believe the earliest catalogue to survive, "Things the Soldiers are Asking For!" dates to December 1914 (reprinted by Briar Books Press a few years ago), and it has the earliest shape chart I've seen. This does depict a
very small bent with the shape designation of "55" (which does not appear in the 1920 edition of About Smoke); so it may have been eliminated during the period that Dunhill is believed to have largely ceased using French sourced stummels in their manufacturing operations). You
definitely have a 56. Which also happens to be one of my longstanding favorites. (Indeed--to confess all--I own five, dating to 1920, 1932, 1949, 1952 (unsmoked), and 1969--all of them acquired during a six month period 15 years ago).
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