Factual error: Declan takes a gun from his glove compartment and nothing else. I counted that he fired 22 shots before being put down. There is no way that gun had a 22+ round magazine.
Factual error: In the opening heist, the gang of thieves wants to steal "The Medal of Zeus." A plate at the museum explains that in Ancient Greece, Olympic champions were awarded olive wreaths, up to the 88th Olympics in 424 BC, when a golden medal was given to the victor for the first time. This last bit about gold medals is just made up by the movie. But it also gets the timeline wrong; the 88th Olympics were in 428 BC. 424 BC is when the 89th games took place. (00:03:30)
Factual error: When Joseph Gordon-Levitt is playing poker, they are using Morgan style silver dollars. The stacks of dollars are treated as $100 dollars. But a Morgan dollar is 2.4 mm thick, a hundred dollars would be 9 .44 inches high and the stacks of coins were about half of that. (00:11:00 - 00:12:00)
Factual error: Near the end of the helicopter scene Jenko pulls the pin of a grenade with his teeth before he throws it. It is not possible to pull a grenade pin with your teeth as it requires more force than that.
Factual error: After the introduction, there's a scene supposedly happening near Lausanne on the Lake Geneva, but in fact it's altogether the wrong canton, Ticino and most likely Laggio Majore, a couple of hundred kilometers away. (00:06:00)