These two stamps were never used on postage (or telegrams, or duty). In line with many countries at the time, their purpose was to encourage the public to invest their money with the Government to pay for the war. Theoretically, they have no place in a stamp handbook (or collection). However, they assume their own importance in describing the first definitive issue.
On the outbreak of World War I, Harrisons experiment was abandoned. It is most likely that but for the war, recess printed postage stamps would continue to be produced, as a matter of policy, by Harrison, at the Note printing branch.
Harrisons printing equipment was under utilised. There were only so many banknotes in circulation. Whereas Cooke was flat out just keeping up production of the standard letter rate. 2 million stamps per day were used and discarded.
When it came time to create the war savings series (2 stamps of 6d and 2/6d respectively), Harrison resurrected his existing designs, layouts and printing machinery to that end. The same plate format of 12 x 10, with imprint and plate numbers were used. As an expedient, the die of the existing (but cancelled) 2d recess was modified to create the 8 plates. (quad plate printing).
This brought to a temporary end Harrisons involvement with stamp production. Four years later, in the last year of the war (May 1918) Cooke retired. Harrison (Cooke's boss) took his place at the helm of surface printed KGV/Roo issues.
The recess experiment was over. 14 years later, in May 1927, Harrison resurrected this method, with the Parliament house Commemorative.
The watermarked paper used for this issue was that specially imported by Agar Wynne intended for the original series but not used as such.