Changes only HCM Extract for Employee Assignment does not pull records correctly

Summary

Changes only HCM Extract for Employee Assignment does not pull records correctly

Content

We have a custom Changes only HCM extract to pull Employee Changes for past 180 days and future 15 days. Initially we have used Assignment Id and Effective End Date as key attributes but as we were seeing discrepancy for future dated transactions  we then made Assignment Id as the only Key attribute for Assignment Record in PER_EXT_SEC_ASSIGNMENT_RANGE_UE. We still see some discrepancies. 

To create a Assignment Record in UE-PER_EXT_SEC_ASSIGNMENT_RANGE_UE, what should be the Key Attributes on the Assignment Record considering we need to send employee changes for the past 180 days.