GB_RATES_HISTORY function not prorating for mid-month spinal point changes

 1. We are using seeded GB_RATES_HISTORY function in our Basic Salary calculation
2. We have spinal points
3. It is working correctly for normal salary calculation, prorating correctly for starters and leavers but it
is not prorating correctly for mid-month spinal point changes

Example:

1. Employee is Spinal Point (19) (Salary: 21843). This gets changed to Spinal
Point (20) on 16-Feb-2009 (22631)
2. When I run the Quick Pay, it shows salary as 22631/12 = 1885.92

Formula that I am using is following:

IF prorate_start WAS DEFAULTED

  THEN ( prorate_start = PAY_PROC_PERIOD_START_DATE )

 

IF prorate_end WAS DEFAULTED

  THEN ( prorate_end = PAY_PROC_PERIOD_END_DATE )

 

days_in_month = days_between(PERIOD_END, PERIOD_START)+1 days_worked = days_between(prorate_end, prorate_start)+1