Goofs

The triple scar on Samantha's arm keeps jumping from left to right arm and back.

Johnny opened Cobra Kai under the belief that Kreese was deceased. In The Karate Kid Part III (1989) it was established that the dojo was a subsidiary of Terry's company. Therefore Johnny would not have been permitted to use the name without Terry's permission.

Brand names, if not used in any way, shape, or form for a prolonged period of time are officially up for grabs.

About halfway through the season, the tournament committee decides to change the tournament and add "skills tests." One of the skills is the use of weapons. However, weapons do not exist in Karate (the word's meaning is "empty hand"). Instead, they are adding a new martial art into the pile, called Kobudo, which is considered a sibling to Karate, but not as popular.

Amanda finds out that Kreese had a Personal Protection Order instituted against her when she and Daniel go in to get one against Kreese. The desk sergeant confirms she can still fill out the forms, but he states that it wouldn't mean much since it means they have to stay a distance away from each either way. In actuality, the PPO only prevents the person named to not approach; the petitioner is free to go anywhere. By getting one herself, Amanda would be able to prevent Kreese from approaching her or abusing the PPO by forcing her out of locations like he does at the town hall meeting. Had she not gotten the PPO, Kreese could legally enter the LaRusso dealership and force Amanda to leave before she would have the ability to call the police on him to have him arrested and cited for trespassing. The PPO would also give the LaRussos more standing to pursue harassment charges against Kreese for planting a cobra in one of their cars or sending a gang of his students to break into their house to start a fight.

During the Vietnam flashback sequences, one of Kreese's closest friends in his unit is a soldier who goes by the name of Ponytail, due to his ponytail. Having such long hair is explicitly prohibited by US military regulations. In some outside chance Ponytail had managed to get away with this, a superior (especially Captain Turner) would have forced him to cut his hair.

Many people believe that Miyagi's name on his headstone is a continuity error, given that in The Next Karate Kid (1994) his name is stated to be Keisuke, but it was actually shown previously on a sign being held for him by Chozen in The Karate Kid Part II (1986) to be Nariyoshi. This means that it was The Next Karate Kid that changed his name, while Cobra Kai kept the name previously given for him.

Another interesting fact, however, is that the name given in The Karate Kid Part II was not the original first name given to Miyagi. In The Karate Kid (1984), it can briefly be seen on Miyagi's dog tags, attached to the keys of the 1948 Ford given to Daniel for his birthday, that Miyagi's first name is Hideo.

When Eli ("Hawk") changes his hair to a spiked mohawk, his previous hair isn't nearly long enough to go that high.

In Season 1, episode 5, Daniel attempts to raise the rent of Johnny's dojo which he explicitly states Los Angeles neighborhood of Reseda. Prior to this, all of the fliers for Johnny's dojo say that it's in the Van Nuys neighborhood. However, since the two cities are not large and right next to each other it makes perfect geographic sense.