The movie takes place in 1944, but in the diner scene a picture hanging on the wall shows muscle cars from the '60s and '70s. Corrected in the home-video version.
When the Germans go out to harvest the corn they are given long-handled knives or scythes, but corn picked by hand was picked with a leather glove with a metal hook in the palm. The ears of corn were then thrown into a wagon and taken to be dried and stored.
A small-town Iowa cafe in 1944 would not have an aluminum-framed door, those tables and chairs, or those coffee pots with orange and green plastic spouts for regular and decaffeinated coffee.