The reported dates are when the database has first picked up the applicant at that address and when they were last picked up there. There tends to always be an overlap.
Tracking a renters address history is much more difficult than someone who owns a home. In a homeowner scenario there are public records and a history of official filings (deeds, assessments, etc.) that help track exact dates. Since renters have no official filings, the databases must use information like tax filings, postal services, and credit applications to track what addresses are being used and when.
Because tracking a renters address history is not an exact science, it is the only portion of the background check that contains the disclaimer "this information should not be used as a basis for adverse action". In other words, you should not deny an applicant based solely on this information.