If they are meant to depict history the films should stick to the facts. Sometimes for plot continuity dialogue may have to be created. Such dialogue should be true to the nature of the historical characters portrayed. Even non-war films prtraying major historical events should follow these principles.
Some films, such as “Private Ryan” and “Kelly’s Heroes” portraying sideline events can take some liberties but the larger context shoud be realistic. A historian cringes when seeing wrong uniforms, vehicles, weapons, etc. Sometimes practical necessity has ruled, such as “Battle of Britain” where there simply were not enough Bf-109E’s in existance, so later models, including some made in Spain and Czechoslovakia after the war had to be used.