This card may look like an odd one out but if you go right to the start of the realm of Middlesex, Westminster was part of its lands. That makes it doubly galling that it was Westminster that allowed Middlesex to disappear.
There are actually three versions of this set. All were issued in 1937, but our British Trade Indexes say it most concisely, as :
CEREMONIES OF THE CORONATION. Sm. 67 x 33. Nd. (25) ... MBM-1
A. Caption on front in black, back in black
B. Caption on front in blue, back in black
C. Caption on front in blue, back in blue.
Now in some dealer lists this is different. They list a black back and blue caption, which corresponds to B, and one with a blue back, which is possibly C. However they then sometimes have a version with a black back and a brown caption rather than the black and black. I have not seen the “brown” so if anyone has one do send us a scan please.
By the way, this is why when ordering varieties and different printings, it is always best to add a full description in words as well, rather than just go by the letter given.
As far as scarcity it seems that the blue front and back (our C) is quite a bit more expensive, so it must be rarer.