They did release both Ancient Art of War games before the Manhunter series. This is from Sierra´s Tenth Anniversary catalog (1989), page 32:
“Dave and Barry Murry got started designing computer games in 1980. They designed an air traffic control simulator, but decided that games would be more fun. When IBM released its first PC, they developed ‘Sierra Championship Boxing’. After the success of their games ‘The Ancient Art of War’ and ‘The Ancient Art of War at Sea’, Ken Williams asked them to do a game using Sierra’s Adventure Game Interpreter system. In 1988, Sierra released the first in the horrorific Manhunter series, ‘Manhunter: New York’, designed by Dave, Barry, and their sister DeeDee Murry.”