Four different styles of number were used to make up the overprint and consequently here are four types of overprint.
Type A
Type A has a narrow figure 4 with serifs.
Type B
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Type B uses a sans-serif 4 with pointed top and left.
Type C
Type C uses a sans-serif font with the top and left points of the 4 truncated.
Type D
Type D is a wide figure 4 with serifs.
Forgeries
Some forgeries of this issue are illustrated here.