David is supposed to be the brother of Kurt and Eric from the first movie, but his last name is spelled differently (Sloan instead of Sloane).
During the Brian Vs. Tong-Po fight, Tong-Po lifts the referee onto his shoulders while wearing a pair of boxing gloves. Yet when you see the referee being thrown over the top rope and out of the ring, you see him being thrown by a bare pair of hands.
When Jack quickly disarms Sanga's bodyguard near the end of the movie, the bodyguard doesn't flinch or even makes eye contact with Jack. He stands perfectly still while staring into the distance until he is punched and knocked down.
When David delivers repeated kicks to Sanga (Tong-Po's manager), Sanga's face is covered in blood during the face-kick, but the blood has disappeared in the next frame during the groin kick, and then re-appears during the next kick.
There is no way Tong Po could have killed Brian in the ring. In reality, after the referee ended the fight and Tong Po elbows him in the gut, the ring would have been swarmed by security but instead he is allowed to casually continue pummeling Brian.
During the opening credits, a picture is seen of David with his two brothers, who are clearly different actors than from the first movie.
When David delivers the final kick to Sanga, he raises his left leg to kick but in the next frame it is clearly his right leg which comes out and makes contact to Sanga's face. The right-leg is also a prop made of rubber as you can see the crews hand holding onto the thigh part and the rubber foot flopping/wobbling when contact is made. The following frame shows David bringing back his left leg after the right-legged kick.
During the flashback when Sangha tells his goon what happened to Kurt Sloan after Tong Po battled him, a water machine is visible at the top of the screen spraying out a rain-like effect.
David and his manager talk about taking some exhibition kick-boxing bouts like Kurt used to take. This is impossible, because Kurt Sloane never competed in kick-boxing in US. Even though he did have previous martial arts experience, his background was in karate, not kick-boxing. He only had two kick-boxing matches before he was gunned down by Tong Po, and both of them were in Thailand.
It is said that David is the brother however, no mention of a third brother is mentioned in the original.