Madame Joseph fake postmark

I bought this stamp with a GPO/BNB postmark recently for I thought was a very fair price. On closer examination, it has a date stamp of 22 AUG 1911 which unfortunately correlates with one of 5 known date stamps of Madame Joseph for North Borneo. The others include a double ring Sandakan postmark dated 16 JAN 1916, 2 double ring Jesselton postmarks dated 22 AUG 1931 and 22 AUG 1941 and lastly a single ring post-war type Jesselton cancellation with the date of 15 JA 48 in one line.
Madame Joseph operated from premises near to Charing Cross Road in London in the early part of the twentieth century. In all there were over 400 different fake cancellers which were also sold or rented to corrupt dealers who used them to manufacture more valuable postmarked copies from cheap mint stamps.  They were mostly applied onto commonwealth stamps. When she died, her post marking equipment passed through various hands, the most recent date of one of her fake cancellations was1967. Eventually, they were bought up by The Royal Philatelic Society of London to prevent further use of the equipment. They also publicised the existence of these fake postmarks.