North Borneo 1916 4c carmine Maltese cross perf 15

The 1916 4c with carmine Maltese cross overprint was not listed in Stanley Gibbons catalogue until about 10 years ago. This is surprising because it was mentioned in the definitive text "The stamps and postage history of North Borneo" part 3. However a perforation 15 variety is not mentioned anywhere.

The Maltese Red Cross overprints were issued in aid of war charities. They exist with vermilion and carmine overprints. The overprinting was carried out by Waterlows in London. A limited quantity of stamps were overprinted. They are consequently  uncommon especially genuinely used or on cover. Copies of this issue with CTO bar cancels are generally considered to have fake overprints. Mint or used stamps with fake overprints can be very difficult to detect.