Continuity mistake: When Bruce Lee and Han first jump up at one another, Han slashes Lee across the stomach with his 4-knife hand, but Lee only has 3 blood scars across his abs for the rest of the film.
Other mistake: When Williams fights Han's guards in the office, at one point he kicks a guard back towards a window, the guard stumbles and then for no reason just dives backwards out the window. A bit over dramatic.
Factual error: When Han is fighting Williams, Williams throws a side kick to Han. Then he lifts up his hand to block - supposedly a metal hand - but his hand does not move one bit. It is not possible, due to that kind of force, for a hand to not move. Even if a hand is metal, the elbow will pivot. As well as the fact that after the kick, you see Williams' face is in pain. This is not possible as he is wearing soled shoes and kicking side on.
Answer: Yes, he filmed all of his scenes before he died. He died on July 20, 1973 - only six days before the film debuted in Hong Kong, and only a month before the film's US debut.
TedStixon