Hannah's camera is not equipped with a flash but she still takes photographs at night and indoors with the resulting images perfectly exposed. In actuality, she would have needed a flashbulb for lighting.
Comets don't shoot across the sky like that.
Hannah tells the police in the present that her husband bought their Hudson before the war, but the car is no older than a 1945 model, which came out in August 1945.
When Hannah gets the car stuck in the snow, the parking lights are both working with the headlights. The didn't do that in 1942.
The characters go on to continually comment about Hannah's 1945 wardrobe but when she climbs out of the storage shed window, she is clearly not wearing 1945-era stockings which would have had seams and reinforced toes and heels. (If they really wanted realism, war rationing would have dictated that those stocking be made of rayon which notoriously bagged at the knees and ankles).
The opening of the film is set before Christmas 1945 and the newsreel in the theater mentions the 82nd Airborne Division in a parade in New York City. Troops from the 82nd Airborne Division were part of the New York City Victory Parade, but it was held on January 12, 1946.
Hannah's hair & curls would change from tight and stiff to stretched out and almost flat.
Hannah tells the police in the present that her husband was at war in France more specifically in Malmedy but Malmedy is in Belgium.
Hannah's friend, Dottie, appears as a young nurse with light blue eyes. When Dottie later appears as an elderly lady in a nursing home, her eyes are dark brown.