LSAL & Effective Date

We are using LSAL to track Salary rounded up to the next thousands.  The DBA is set to pull LSAL and FAGE.  My Benefits Self Svc Constants are set at 1/1/11 for FAGE and 10/1/10 for LSAL.  When I Build Workfiles, the calculated amounts are based on the LSAL in this field at the time of the build (i.e, both Current and Available are the same.  If I populate LSAL with the new amounts, both workfiles contain calculations based on the new LSAL.  History is being tracked for LSAL. I want DBA to calculate based on history so that if history shows