A gold bar that size would have been way heavier than shown in the film. Kessel states the gold bar is worth $42,000. At an average price in 1971 of $40.80 per troy ounce, that would make the bar weigh over 70.6 pounds.
At 00:01:15 "Filmed in Hamburg, Bavaria and Scandanavia..." - seems a popular mistake but it's "Scandinavia".
The smooth-talking drug dealer with the dark beard states that the Candy Man had "brought in six kilos" of heroin on his previous trip. Yet the Sarge indicates that the Candy Man transports a standard lot of 24 baseballs --- filled with four ounces of heroin apiece, or 96 ounces total --- on each smuggling trip. This would amount to a smuggled-drug total of only six POUNDS, not kilograms, which are over twice as much weight as pounds. So for the Candy Man to have actually transported six kilos (at 2.2 pounds for each kilogram) of heroin inside baseballs, he would have needed to have carried 53 baseballs at a time, not just 24.
At about 70 minutes into the movie, Goldie Hawn is called in a public phone booth in Hamburg by Warren Beatty. The film takes place around 1970. While a public phone booth could always have been called in the USA, in Germany it was not possible until 1983 when about 300 booths were retrofitted accordingly.
"If the pick-lock key had fallen into Joe's pant-cuff instead of the floor, it would not have made a clink." The key could have easily bounced off the floor and landed in the cuff.
Obviously "empty" car (i.e., no driver) used in the shot where it falls through the ice.
After the alarm at the bank over the gold bar incident, as a police car pulls away, a reflection of the camera is visible in the rear passenger side window.
No effort is made to warn Joe about the use of the thermal lance (aka burning rod), and the fact that when it breaks through into the vault, it will be spewing out a stream of molten metal into said vault.
In a televised interview, Mr. Kessel speaks of Joe's carrying "the gold bars" to safety, when in fact there was only one bar.
Joe identifies the vault's door as being "eight inches of tempered steel", but the door is clearly a lot thicker than eight inches.
It appears that there was an error in Sarge's calculation of how much the Candy Man's heroin-filled baseballs were worth: if "one baseball is worth $19,000, and the Candy Man has prepared 24 of them", then $19,000 multiplied by 24 is only $456,000, not $470,000. Each baseball would have to be worth $19,583.33&1/3 for 24 balls to be worth $470,000.