I think I may have just found the missing link.
Have a look-see:
http://cgi.ebay.com/Vintage-1964-Kay-Tr ... dZViewItem
18 Frets AND a pointed horn... branded under the Truetone label.
So now we've got:
... 18 Frets, NO truss rod adjustment, and a rounded horn...
... 18 Frets, truss rod adjustment, and a pointed horn...
... 19 Frets, truss rod adjustment, and a pointed horn.
Honestly, I'm just thinking they kept re-designing the Demon over a few short years, following the trends. If you follow Kay designs, you can see their catalog models get generally "pointier" as you go through the 60's... especially in models like the Jazz II and the "Kessel"... both DC's... but man did that later Kay Kessel get pointy.