The Work History tab in an applicants record is intended for keeping a record of their past pre-RDB work history as well as placements made in RDB. The client employee history shows the same information but from the client's perspective.
This history is separate data from the Placement Index, so when a row in an applicant's Work History is deleted, that action doesn't delete the actual placement. Rows can be added to the Work History to record any placements not already showing up as follows:
Open the Applicant record.
Click on the Work History tab.
Fill all fields as appropriate, in particular the Placement field (choose the placement by clicking on the [...] button).
Click Save and Close.
Repeat as necessary.