The suffixes are:
BK = Booklet Pane;
BK OP = Booklet Pane Overprinted for a Show, Expo or Special Event;
a BK = Booklet Cover;
a BK OP = Booklet Cover Overprinted for a Show, Expo or Special Event;
BX - Issued box of stamps (can be a 100 or 200 roll of stamps), generally Peel & Stick type;
C = Cinderella or stamps with No postal validity;
CB = Cheque Book (usually 20 Booklets, stapled together)
CP = Counter Printed stamps (Computer generated at the counter)
GS = Gutter Strip;
MS = Miniature Sheet;
MS OP = Miniature Sheet Overprinted (a miniature sheet overprinted for a Show, Expo or Special
Event)
OF = BCOF or British Combined Occupational Forces, Japan;
OP = Overprint on an already issued Booklet, Miniature Sheet or Sheetlet;
OS = Large Punctured OS or Official Service;
PB = Prestige Booklet;
PC = Complete Normal Pane;
PCR = Complete Reverse Pane;
POS = Printed OS or Official Service;
SESS = Special Event Souvenir Sheetlet;
SH = Sheetlet of 5, 10 or 20 stamps;
SOS - Small Punctured OS or Official Service;
SP = Stamp Pack (an officially packed set or group of stamps)
SPEC = Specimen Overprint (all types);
SS = Se-tenant Pair, Block, Set or Strip;
TB = Tete-beche Pair, Block, Set or Strip;
VP = Vertical Pair or Strip (the same as SS except in vertical format).