1920-24
These stamps are watermarked "Mult Script CA" which was introduced in 1921. From the reverse it looks like this:
A newly shaped crown and CA in script character.
SPECIMEN overprint on the 1921 "Mult Script CA" stamps: Samuel Type D12
The De La Rue Overprint on these stamps is Type D12: Length 14.6 mm, Height: 2.5 mm.
The black spot inside the left leg of the M occurs in position 5,23,53 and 59 (Column 5 in the 60 set overprint, but column 3 in the NH 1911 & 1921 specimen stamps).
Information thanks to Jeff Blinco.
In 1921 three denominations of the English issue were printed on the new Mult. Script CA Watermark paper.
Engraving: Leonard Vincent Phillips
Design: J. Giraud
Printing: Thomas De La Rue & Co., Ltd.
First Day: August 1921 ♦ first day recorded: 18 August 1921
Perforation: 14
This series exists with overprint "SPECIMEN".
The 1921 British Watermark Mult. Script CA stamps
S.-G.: 36-Yv: 71
Sc. : **-Mi: 74
S.-G.: 37-Yv: 70
Sc. : **-Mi: 75
S.-G.: 39-Yv: 72
Sc. : **-Mi: 76
The 1921 British Watermark Mult. Script CA Specimen stamps
S.-G.: 36s-Yv: --
Sc. : **-Mi: --
S.-G.: 37s-Yv: --
Sc. : **-Mi: --
S.-G.: 39s-Yv: --
Sc. : **-Mi: --
Quantities: 1d: 90,000 ♦ 2d: 90,000 ♦ 6d: 15,000 ♦ Specimen: 420 sets
The 1921 British Watermark Mult. Script CA Specimen stamps from the Madagascar archive
From the Madaagascar archives: 1921 Specimen set with the "Broken M". (Blinco coll.)