Beautiful gorgeous and droolworthy!
Great work there Al.
I agree with you about the oddity of the stem and I have no idea if the factory ever made them that way. That particular "negative" diamond P logo is also of the more rare variety, much less seen than the usual P stem logo, and goodgoddamighty it's still got the Pat. # onnit too! Those markings are usually rubbed/buffed away to wonderland on the stems. An incredible pre-war example of a Parker, back when they were actually closer to the quality of a Dunhill, as in the post-war years that quality began a steady decline.
I have an intense interest in Parker pipes, however, I only have 2 at the moment, one is a 1949 Briar Bark billiard though, these old Parkers are difficult to come by because it seems there just ain't many around to be found, and alotta collectors go for 'em, so then the $$$ gets outta my range, and more often than not the older specimens have been smoked as hard as hells chimney!
I have contacted the well-known Parker expert Michael W. Reschke for some specific info once and he's as gracious and gentlemanly as can be, an enthusiast proper, and quickly responded to my inquiry. I contacted him via his ebay account, he may offer knowledge if you seek further detail.
http://www.ebay.com/usr/mwreschke
I believe the PAT N° 116989/17 was a UK Dunhill patent for the flanged style of innertube.
Also, dig this very scarce 1942 Parker, Michael Linder provides a great deal of info in its description:
http://www.thepiperack.com/blue-chip-estate-pipe-parker-super-bruyere-patent-rarest-1942-19-date-code/
Again, great work.
If you do indeed go Sherlocking, please let us know if you discover the significance of the "negative" P logo!