All Federal employees undergo checks of the accuracy of their applications. For most employees these are carried out by the Federal Investigative Services of OPM. That office mails a computer readable form to the person given as a reference by the employee.
For almost all employees, the same reference is contacted to verify more than one item, such as multiple previous employers or multiple previous residence addresses. But each inquiry is mailed in a separate envelope (with $0.365 postage) and includes its own separate postage paid envelope for response.
For example, last week I received seven different mailings from OPM for confirmation of statements by the same employee. It would seem a simple matter to program a computer to consolidate the questionnaire to cover all items in a single mailing. The paper and postage saving should be substantial, and only a single reply would need to be processed instead of many.