Why does merging of candidate and ex-employee withdraw the candidate from the application?

Summary:

With our university campus program, we hire a lot of interns. When the internship is over, they are inactive in Person Management. If a full time offer is extended and accepted, the ex-employee is found during the duplicate check and the candidate is merged with the ex-employee and the application for the full time position is moved to a withdrawn state.

This interferes with reporting, as we are trying to get accurate data on start dates for new grad (full time) positions, but because the application is withdrawn, it pulls the start date from the previous (intern) application, which is a date in the past. And if we code the report to include withdrawn applications, it will pick up candidates who have actually withdrawn.