Dating a parker duofold
Setting up a new production line staffed by former ink workers, it would only have made sense to give the pens coming off that line a distinguishing mark to facilitate troubleshooting and quality control, which could be eliminated once the new line had proven itself to be running as smoothly and reliably as the old.And that's exactly what we see when we count the numbers of "T" marked pens over their five quarters of production.
That factory building had been acquired by Parker in 1935, and was still popularly known by the name of its previous owner, Townsend Tractor.
T-marked 51s are found in the USA -- not in Canada or British territories -- nor do they exhibit any of the subtle differences that distinguish Canadian 51s from their US-made equivalents.
At the time the T code was in use, the postwar surge in demand for 51s was outstripping Parker's production capacity.
The exception is late-production Vacumatics, assembled and date-coded in very small numbers into the early 1960s (late Canadian production was significantly greater, with pens typically bearing a single-digit date code in a much larger font than that used for USA pens.
A similar date code may also be found on other Canadian-made Parkers of the same era.
These seem to be the result of Parker clearing out stocks of old parts, assembling them into pens years after they were originally produced.