Balance Adjustment effective dating

Summary:

What is the appropriate date to use for a balance adjustment?

Content (required):

I have some balance adjustments that I need to enter for prior quarters....some are for terminated employees. We use ADP to process our payroll, so I will be doing the amendment through ADP. However, I need to update Oracle so that the information there is accurate, as well.

The information I found about balance adjustments indicates that it should be effective dated sometime within the the defined payroll period. Is that the pay period that the incorrect amount was entered or the current pay period? If current, how can I correct a terminated employee without rolling back payrolls that were processed since that time?