I can’t speak for past iterations of the Authentic line, but the recommended strings for the current D-18 Authentic 1937 are ‘Authentic Acoustic Lifespan 2.0, Phosphor Bronze, Medium’, i.e. 13-56. I believe I’m right in saying that this model also has a fixed (non-adjustable) truss rod.

It should be remembered that truss-rods have nothing whatsoever to do with the need, or otherwise, for a neck-reset.