When Dr. Johnson and Snapshot are trapped behind German lines during the Battle of the Bulge, Snapshot asks if they should try to go towards Cologne (Germany). At this stage of the war, Dec. 1944, the allies had not yet crossed into Germany, except in one or two places, and only in toehold positions.
At the end of the film. Penny Johnson says she followed his (her husband, Clark Gable) movements on a map. During World War II people in the military had it drilled into them that could not say anything about where they in letters sent back home. And to make sure they kept that rule. The mail from soldiers was heavily censored. This has been mentioned in numerous histories of World War II. And my own father's experience with this backs this up. He sailed all over the world during the war and the censors made no attempt to mask the fact that they had opened and read mail. So my mother started sending my father a stick of gum in letters to him. But, she always included two. One for the censor and one for my dad. And most times. That second stick was gone. And with Gable being an officer it's even less likely any information about his movements around Europe would have been available to his wife.