Factual error: At the end of the movie, a pack of Lucky Strike cigarettes is shown on Ness' desk. The circle on the pack is red. Before America entered World War Two, Lucky Strike cigarettes had a green circle. The red circle was added with the ad campaign, "Lucky Strike is going to war."
Suggested correction: This entry is wrong.
While the correction could stand to be more specific, the entry is wrong. The Lucky Strike circle has always been red. The redesign came from switching from a green box to a white box (which Lucky Strike marketed the change as a way to support the war). The pack seen on the desk is green, indicating it's before WWII.
Question: How accurate is the portrayal of the Untouchables, when it comes to names and numbers? Were there actually only four of them? Do Garcia, Connery and Smith play actual people or fictive ones?
Answer: It's about 50% truth and 50% fiction. Ness, Al Capone, and Frank Nitty are real, of course, but the characters played by Connery, Garcia, and Smith are fictional. Ness started out with 50 candidates for his 'Untouchables' force. This was whittled down to 15 finalists and from that he selected 9 agents (none of which has the same name as the characters played by Connery, Garcia, and Smith). It's true that Capone was convicted for tax evasion. He was sentenced to 11 years in prison, but received an early release because he was in the last stages of syphilis. He died shortly after being released from prison.
Capone lived for 8 years upon his release from prison. The 8 years being slightly longer than the actual prison time he served, which was just over 7 years. He died, having the mental capabilities of a 12-year-old.
Factual error: The film shows government agent Eliot Ness throwing Al Capone's right-hand man, gangster Frank Nitti, to his death from the roof of the Chicago courthouse in 1929. It never happened. Frank Nitti died of a self-inflicted gunshot wound in 1943.
Suggested correction: The movie was not meant to be exactly like real events. The movie was loosely based on the events (aka "inspired by actual events"). There are a lot of differences between the movie and the real events, these were done on purpose, to make an exciting movie.
That's a lame excuse. There are lots of opportunities to embellish on the truth when dealing with a historic topic. The station scene with the baby is an excellent example of that. But, you can't go changing the relationships of main characters or the time and methods of their deaths. Especially ones so well documented like Capone and Nitti. Why even bother using real names? The character they called "Nitti" was just a completely made up character. Nothing about him resembled the actual Nitti. Nitti wasn't skinny and he didn't wear white suits. He wasn't a loner, often scene hanging with his crew. Nitti was an exceptionally short man with a Chaplinesque moustache. Always jovial for the cameras.
It's simply your opinion that it's a "lame" excuse. The fact is the film is highly fictionalized. It's not a documentary, it's a drama. They combine and eliminate characters, give them different names and characteristics, and show events that never happened. These are not mistakes, they're known as creative license. They would only be mistakes if they film claimed everything in the film was true and accurate to history.
While calling something a "lame excuse" isn't acceptable, the mistake is still valid. The film isn't set in an alternate timeline, so historical inaccuracies regarding real life people are considered valid mistakes. Artistic license extends to adding things that could have happened that didn't impact historical events for dramatic purposes (love interests, made up characters, etc). Historical inaccuracies regarding real life figures would be the same as pointing out anachronisms in a film set in the past, like have a car from the 40's in a film set in the 30's. And just because a screenwriter or film maker wants to change facts to make the film more exciting doesn't mean the mistake is no longer valid.
Might as well toss the whole movie with your logic. Ness was never an active agent and never had any contact with Al Capone. Like already stated, this isn't a documentary, so expect some creative license.