Here is a chart with payroll codes used by the DOE:
Differentials:
MA – C1 NA – C1 with PD
PA – C2
QA – C2 with ID
RA – C2 with PD
SA – C2 with ID
TA – C6
UA – C6 with PD
Longevity Codes:
A or B – under 5 years
V or W – 5 years but less than 10 years
C or D – 10 years but less than 13 years
G or H – 13 years but less than 15 years
E or F – 15 years but less than 18 years and PD
I or J – 18 years but less than 20 years
K or L – 20 years but less than 22 years
M or N – 22 years or more