Documents show U.S. officials believed they did.
Kissinger List -- of 82 PWs not returned during Operation Homecoming, with memo from the Senate Select Committee on POW/MIA Affairs
Information Pertaining to PW/MIA Situation in Laos -- Memo for the Chairman, Joint Chiefs of Staff from Lt. General John R. Deane Jr. USA Acting Director Defense Intelligence Agency
U.S. PW/MIA Personnel in Laos -- Memo from Assistant Secretary of Defense Lawrence Eagleburger to Secretary of Defense Elliot Richardson
U.S. POW/MIA Personnel in Laos -- Memo from Secretary of Defense Elliot Richardson to the National Security Advisor
National Security Council Memo -- from John Holdridge and Richard Kennedy commenting on the Richardson Memo
PW of Whom PRG/DRV Should Have Knowledge -- Lists 171 unreturned POWs, based on returnee debriefs
Memo of Conversation -- between Dr. Roger Sheilds, Assitant Secretary of Defense and John Berbrich of the Defense Intelligence Agency who wrote the U.S. "should not be so adament in denying that there are no U.S. POWs in SEA (Southeast Asia)"
July 3rd, 1973 -- Memo prepared for the Chief U.S. Four Party Military Team - Request for "Additional MIA/BNR Informtion" The memo names servicemen listed in catagories Last Known Alive, Probably Died in Captivity, Died in Incident and Probably Captured, along with brief incident description.
Good Cases -- "List of U.S. Personnel on Whom Their is Survival Evidence."
Hard Cases -- List of U.S. Personnel Captured by the Enemy and on Whom the Enemy Would Have Knowledge - "Hard Evidence indicates they were still alive at another location other than their capture point."