Just posted this as an answer to another question, but thought it may be of interest to others as well...

These are the standby priority codes used:


1 HKFR SAME AS HKF ONLY EP/PM/GM/MM/FO
2 HKF CONFIRMED PASSENGER FOR WHOM THERE IS NO AVAILABLE SEAT IN THE FIRST CLASS CABIN.
3 HKCR SAME AS HKC ONLY EP/PM/GM/MM/FO
4 HKC CONFIRMED PASSENGER FOR WHOM THERE IS NO AVAILABLE SEAT IN THE BUSINESS CLASS CABIN.
5 HKDL CONFIRMED CREWMEMBER OR MECHANIC WITHOUT SEAT ASSIGNMENT.
6 HKR SAME AS HK ONLY EP/PM/GM/MM/FO
7 HKI USE ONLY WHEN PAX HAS BEEN AFFECTED BY AN IROP.
8 HK CONFIRMED PASSENGER FOR WHOM THERE IS NO AVAILABLE SEAT INCLUDING CONFIRMED PS / PS-Y PASSENGERS.
9 HKV CNFRMD PASSENGER WHO IS WILLING TO DEPLANE OR GIVE UP THEIR SEAT ON AN OVERSOLD FLT.
10 A1R SAME AS A1 BUT EP/PM/GM/FO/MM ONLY
11 A1 CFMD FULL FARE PSGR DESIRING CLASSCHANGE ON SAME FLT. INCLUDES PAID F/FFY FARES /SEGMENT UPG/ ALL UPG CERTIFICATES WITH FULL F/C/Y AND B06 FARE TICKETS
12 EP EXECUTIVE PARTNER ON DISCOUNT FARE OR FF EARNED FIRST CLASS TKT CONFIRMED IN COACH AND DESIRING UPGRADE.
13 PM PLATINUM MEDALLION ON DISCOUNT FARE OR FF EARNED FIRST CLASS TKT CONFIRMED IN COACH AND DESIRING UPGRADE.
14 PMOA AEROMEXICO PAX SEGMT UPGR -PLATINO
15 GM GOLD MEDALLION ON DISCOUNT FARE OR FF EARNED FIRST CLASS TKT CONFIRMED IN COACH AND DESIRING UPGRADE.
16 GMOA AEROMEXICO PAX SEGMT UPGR - ORO
17 FO MEDALLION LEVEL ON DISCOUNT FARE OR FF EARNED FIRST CLASS TKT CONFIRMED IN COACH AND DESIRING UPGRADE.
18 SM NON-ELITE SKYMILES MEMBER ON DSCNTFARE OR FF EARNED FIRST CLASS TKT CONFIRMED IN COACH AND DESIRING UPGRADE. ALLIANCE PARTNER AUTHORIZED UPGRADE.
19 SBUP *PAID STBY UPGRADE PROGRAM*
20 A2 DEATH/EMERGENCY
21 B1R SAME AS B1 BUT EP/PM/GM/FO/MM ONLY* AM/AF/KE * SKYTEAM ELITE MEMBERS
22 B1 INCONVENIENCED OR MISHANDLED BY DL - INCLUDES DL OVERSALE/DESIRINGTHRU/MISCON/CXLD/MISCON FROM DL/OA FLT WITH CNFMD DL SPACE.
23 C OAL INCONVENIENCED/MISHANDLED/ OVERSOLD WITH FULL /F/FN/Y/YN/B06 FARE