FCP = Fluorescent coated paper PVAD = Polyvinyl alcohol acetate dextrin gum
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sd23

Two bands

SD23 - Scotland 5.5p Violet, FCP/PVAD, two 4.75mm phosphor bands (Harrison/photo) - Deegam S55.1.1 - S.G specialised XS43 - Stoneham SC42 - Concise S21

From cylinder 1 [23.1.74]
sd24a_24k

Centre band

SD24a - Scotland 5.5p Violet, FCP/PVAD, 4mm phosphor, centre band, APS perforation (Harrison/photo) - Deegam S55.2.1 - S.G specialised XS44 - Stoneham SC43 - Concise S22

APS perforation from cylinder 1 [21.5.75]

SD24k - Scotland 5.5p Violet, FCP/PVAD, 4mm phosphor, centre band, comb perforation (Harrison/photo) - Deegam S55.2.1a

COMB perforation from cylinder 1 [1976]