1943 David P. Lavietes moves his D&P Pipe Co. to Boone, NC in 1943 for the mountain laurel. (DRB)
http://www.drgrabow-pipe-info.com/grabowtimeline09.html
D&P changed their name to Sparta Pipes in the early 50s
http://news.google.com/newspapers?nid=1876&dat=19830803&id=gWEsAAAAIBAJ&sjid=584EAAAAIBAJ&pg=4702,653780
If your pipe has that patent (issued 1937) I would say it is made from an alternate material than briar treated with 12% boric acid. There was a briar shortage during the WW2 era which prompted some pipe makers to use alternate materials like the burl from the mountain laurel. This trend didn't last after the war as briar was soon available to American pipe makers once more. If I had to guess (and it is a guess) I would say your pipe is probably from the mid to later 40s, though could be from the late 30s since Lavietes was developing the process during that time.
David Lavietes is an interesting guy and was quite the prolific inventor when it came to pipes. This is actually the third Lavietes patent I've read in a weeks time. Two of them were for WDC systems, and this one. I picked up an Old WDC SnapKleen from SamCoffeeMan and it's system was invented by David Lavietes. An early version of what we now know as a "reverse calabash" system. The expansion chamber is actually in the stem on this pipe instead of in the shank. The other oddity is that the tenon is located on the shank and the mortis is in the stem. This allows free access to the expansion chamber located in the stem, making the chamber "a snap to clean", hence the brand name SnapKleen. Very unique system for it's time. Mr. Lavietes invented that in 1932 and was quite the forward thinker.