A Christmas Story trivia: the year

There is a debate about when the film takes place. Evidence seems to point to 1939 because of The Wizard of Oz (1939) references. The decoder ring points to 1940. However, if you look at the calender on the wall (during the first dinner sequence), you can clearly see the first of December falls on a Friday. December 1st fell on a Friday in 1939, not 1940 as was previously accepted.