Deliberate mistake: Rather than using real Bruce Lee footage only for the final fight scenes, so the undisguised Billy Lo's different appearance might make sense after his surgery, the filmmakers instead spliced real Bruce Lee face footage throughout the early film giving the character a constantly changing face from scene to scene.
Other mistake: When the bad guys are taking the cash from the vault, they finish with just 3 duffel bags. Yet there are blocks of cash along all the walls, roughly 25 times as big as what they're taking. With the duffel bags supposedly containing $100 million, there would be tens of billions of dollars for the taking. Their escape route is up the elevator to the roof, and into a helicopter. What bad guys wouldn't take all they could carry?
Continuity mistake: When Wesley arrives at Redvale, he goes down into the vault area. When he turns the corner (just a few feet down from the lobby), he sees the bodies of the slain guards on the floor. The vault area is not cordoned off, not closed to the public, and wide open to view by anyone stepping just a few steps down the stairs. Yet there is nobody anywhere to be seen - despite this being the middle of a workday, and the lobby being busy with people just a few minutes before.
Factual error: When the bad guys collect the $100 million in cash from the vault, it's been laid out in just 2 suitcases. According to US government specifications, that much cash (it is mentioned in the movie that it is in $100 bills) would be a single pile nearly 50 feet high (about 10 times what is shown) and 1,000kg - a full ton of weight.