This is a block which should not exist:

APO stopped making inscription blocks available in 1952 as the demand for these meant that a lot of orphaned stamps were left unsold. This, apparently, created an accounting problem. The sole exception to this, according to ACSC is 266z - the 2/6 aborigine issue, originally printed under KGVI - for which there was an emergency reprinting in 1956.
ACSC list neither plate block, nor inscription blocks for this issue. It is also a bit unusual for me in that it is the only inscription block I have that says "Printed by the Commonwealth Bank of Australia / Note Printing Branch", and has a plate number in addition to the inscription.
Can anyone comment of this unusual item?