Dating
Prior to Word War II, the possessive PARKER'S stamp was used. However, at least some pipes were stamped with the non-possessive as early as 1936.
Like Dunhill, Parker pipes are date stamped, but differently than Dunhill. The Parker date code always followed the MADE IN LONDON over ENGLAND stamping. The first year's pipes (1923) had no date code; from 1924 on it ran consecutively from 1 to 19.
There is no indication of a date code for the war years. Parker was not a government approved pipe manufacturer, while Dunhill and Hardcastle were. During the war years Parker manufactured the "Wunup" pipe made of bakelite and clay. A Parker pipe with a 19 date code has been reported, indicating there was perhaps some production of briar pipes as well, but no dating record.
From 1945 through 1949 the Parker date code runs from 20 to 24 and from 1950 through 1957 it runs from an underlined and raised 0 to an underlined and raised 7.
A little help here from anyone with date code information beyond 1957 would be most appreciated.