GAO said in a July report to Congress that the Army reserve components do not have accurate, complete, consistent and timely information on soldier non-availability rates.
The report indicated that the current review process on the quality of reported availability data is limited in scope and frequency, while the data systems also do not interface and support timely updates.
GAO also found that the Army Reserve and National Guard respectively have 81 percent and 74 percent of their investigations on service-related illnesses and injuries overdue.
The U.S. Army is still in the process of updating its guidance to reduce delays in the investigations and address causes such as soldier noncompliance with information requests, GAO said.
The agency noted that information on the availability of reserve component forces is important due to the potential reduction of size in the active-duty forces.