I have been trying to place this black Permanite Duofold, going over again the Duofold book. It has the same Lucky Curve imprint as the 1926 first year Jade Permanite pen. And the same Lucky Curve nib imprint. But it is longer then either the Jade pen or the previous Duofold I have checked, 14.1cm. There are similarities to the model DQ shown in the Duofold book, launched in 1924; the pattern seems the same, as does the imprint, but the nib does not have the DQ imprint and this pen is Permanite. I know this is not an exact science but help would be very welcome.