David Niven, in his Hollywood memoir Bring on the Empty Horses, claimed that Garbo liked to wear comfortable, loose, sneakers under her costumes where they wouldn’t be seen onscreen. This may have been the origin of her phantom “big feet”.
Snopes is right about actors in the U.S. armed services. I can’t think of a single incidence of a Hollywood actor who was in service in World War II who was given leave to make a Hollywood feature unless in that feature he was portraying someone in the U.S. armed forces. That alone would have ruled out Ronald Reagan for the picture, as he was an officer in the U.S. Army Reserve at the time.