Factual error: In the scene where Roxie is placed in the "paddy wagon" to be taken to Cook County Jail, the prosecutor refers to himself as District Attorney Harrison. However, the court system in Illinois doesn't have district attorneys; rather, they have state's attorneys. The original play by Maureen Watkins correctly calls him a state's attorney.
Factual error: The innocent murderess, Katalin Hunyák, is supposed to be Hungarian. Nevertheless, in Cell Block Tango, she tells her story with a very heavy Russian accent. And when Billy passes by, she begs for help in Russian ("Pozhaluysta" - "Please").
Factual error: As Roxie is being escorted into the murderers' row, Mama and Roxie pass Velma's cell. The dollar Velma gives Mama is a modern one.
Factual error: When Mr. Flynn is in the restaurant talking about the latest socialite arrested for triple homicide, he briefly uses a telephone their waiter provides. According to an antique phone collector's association, there are many errors between the phone and the time period. First of all, that phone's design was from the Bell Tel. Co., and wasn't manufactured until about 1930. Secondly, even if the movie was set in late 1929, the phone has a handset didn't exist until 1937. Thirdly, the phone is brass-plated with an ivory handset; This colour combo was called the "Imperial", and was introduced to celebrate the 75th Anniversary of Bell Tel. Co. in 1951, and was certainly not available in the 20s.
Chosen answer: Pregnancy or lack therof would have been noticeable you think, but I am a size 8(aust) and gave birth 8 weeks early, still wearing size 10 clothes - unless I told people I was 7 months pregant they did not know.