I buy lots of estate pipes and somebody tossed this out on the forum several years ago which I promptly added to the collecting notes I carry on my iPhone.
Many thanks to the original poster.
"Kaywoodie
Serial numbers:
2 numbers indicate 1930s-1950s
3 numbers indicate 1970s-80s
4 hole stinger Kaywoodies are from 1955 or earlier
3 hole stingers were from 1955 until today
And More:
Check the Shape Numbers. If the pipe has a 4-digit shape number, the pipe is probably of "pre-1936" vintage. If the pipe has a 4-digit shape number and does not have the threaded fitment, it is probably from before 1925.
The pre-WWII Kaywoodies had elongated white cloverleaf logos and large screw-in fitments (with the possible exception of the pre-1925 and "export" Kaywoodies, which had no fitments).
Some of the pre-1936 Kaywoodies were stamped (on the shank) with a cloverleaf around KBB. Sometime between 1936 and 1947, the better pipes were marked with a black cloverleaf inside a white dot. However, because many of the pipes in the 1968-69 catalog still show this type of logo, the black-in-white logo merely indicates a "post 1936" vintage.
The cloverleaf logo: the round logo (black cloverleaf in white circle or white cloverleaf in black circle) was first used in 1937. Up until the late 40's this logo was used on all of the upper grades pipes. The concomitant use of the plain white cloverleaf and the disk inlaid logo continued until the early 80's.
Up until the late 1940's/mid 50's, the logo was on top of the stem. After that the logo was moved to the side of the stem.
Current (Italian-made) Kaywoodies have the "white outline" logo."
Dunno if this helps or muddies the waters.
You can always reach out to one of our resident Kaywoodie experts, Gary - used to be known as Irish around here. Gary is to Kaywoodie what our Ejames is to Dr. Grabow. Both are mavens for their specific brands and both are just two of the best guys any of us will ever be fortunate enough to know.
Fnord