Continuity mistake: Mr Miyagi said in the first movie he never taught anyone before Daniel, but he says in this movie that he taught Julie's grandfather.
Continuity mistake: When Eric arrives at the docks and gets out of his car and approaches Ned, watch Eric's car in the background. There's nobody else in view at this point, but you can see that something is being splashed onto the car. In a shot a couple of seconds later, Colonel Dugan and some of the other Alpha Elite boys come from out of hiding from nearby and one boy starts splashing gas onto the car.
Continuity mistake: When Eric pulls up to the docks to fight Charlie he is wearing a vest, as he gets out of his car the vest is still seen, a brief moment later the vest has disappeared.
Answer: Likely the filmmakers deliberately changed the plot details to fit the new storyline, either hoping or not caring if the audience noticed. It's not uncommon for films to do this in sequels.
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