Knob-type door locks model code explanation

For example: 5797PB

The digits indicate the shapes of the knob.

The English letters indicate the finishes or some function.

FINISHES                 FUNCTION
SS: STAINLESS STEEL      ET: ENTRANCE
SP: POLISHED STEEL       BK: PRIVACY
PC: POLISHED CHROME      PS: PASSAGE
BN: BLACK NICKEL         WT: WAFER TUMBLER
SB: STAIN BRASS          CK: CROSS KEYWAY
PB: POLISHED BRASS       IC: INTEGRATED CIRCUIT
AC: ANTIQUE COPPER       ST: SECURITY
AB: ANTIQUE BRonZE ??