Per_Periods_Of_Service Not adding a Row for Voluntary Termination Actions

We have been noticing that certain termination actions are NOT hitting the per_periods_of_service table. For example, if I submit a retirement for myself and it goes to my manager for approval, the table will populate a row with the termination date and the name of the user that approved my termination. However for voluntary terminations and resignations, a row is not being added and our reporting is inaccurate because we are not accurately capturing all terminations. What determines whether or not a row gets created for a termination? We can't find a rhyme or reason as to why some are