nd84
PCP = Phosphor coated paper PVAD = Polyvinyl alcohol acetate dextrin gum
ACP = Advanced coated paper
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Northern Ireland symbol types

Type 2a symbol - The pearls along the crown are separate from each other. Type 2b - The second pearl to the left of the orb is joined to the crown and the first three on the left side of the crown are joined to each other. The bottom pearl underneath the orb is attached to the central cross.

ND84 - Northern Ireland 31p lilac, PCP/PVAD, type 2a symbol (Cyls Q3, Q4) (Questa/litho) - Deegam N310.1.1 - S.G specialised XNL57 - Stoneham U66 - Concise NI64

Type 2a from cylinders Q3, Q4 [23.10.84]

ND85 - Northern Ireland 31p lilac, ACP/PVAD, type 2b symbol (Cyls Q5, Q6) (Questa/litho) - Deegam N310.2.1 - S.G specialised XNL58 - Stoneham U83 - Concise NI64Ea

Type 2b from cylinders Q5, Q6 [14.4.87]