BIRT: Why are FROM_TIME and TO_TIME Parameters missing in WORKITEM_CHNGS?

 The WORKITEM_STATES table has FROM_TIME and TO_TIME parameters to allow filtering by date range.  However, these parameters are missing from WORKITEM_CHNGS.  I have been able to filter this table using a Filter expression, but that is less efficient and has other limitations.  What is the recommended approach for reporting on workitem changes over a specific time period?  Also, is there a reason why the FROM/TO parameters were omitted from this table?