Now that Dragon Ball, it's bound to create some inconsistencies.
Akira Toriyama, the creator of Dragon Ball has made it known many times that he often makes things up as he goes along. This creates a very unpredictable franchise and sometimes, creates some fun retcons for fans to discuss.
The Potara Earrings
When fusion was introduced during the Buu Saga of Dragon Ball Z, the stage was to have fun combinations of certain characters. But a weird dance wasn't the only way two characters could fuse. The earrings that Kai's wore were able to fuse to beings together, but with a major catch: it was permanent. When Goku and Vegeta put the earrings on, it was with the understanding that they would be stuck that way forever.
Except they weren't. When they were absorbed by Buu, they split and Goku just figured it was due to the bad energy within the evil character. But Dragon Ball Super took it one step further by saying that only Kai's can fuse forever and non-kai's would only be fused for an hour. It kind of retroactively makes the dance useless but at least fans aren't in danger of losing Goku and Vegeta to Vegito.
The Origin of the Scouters
Saiyan's weren't the original inhabitants of Planet Vegeta, it was the Tuffles. The Tuffles were exterminated by the Saiyan's who would go on to claim the planet for their own. One piece of technology from the Tuffles that the Saiyan's kept was the Scouters. From there the Saiyans would introduce it to the Frieza Force, but Dragon Ball Super: Broly changed that.
The beginning of Dragon Ball Super: Broly shows the first time Frieza came to Planet Vegeta. Now that Frieza's father, King Cold, was retiring, Frieza was taking over and brought a piece of new technology to the Saiyan's as a gesture of goodwill: The Scouters, meaning they were no longer there first. This change creates a new power dynamic between Frieza and the Saiyans because now the Saiyan's were only good for their strength.
The Reason Why Frieza Destroyed Planet Vegeta
Back when it was revealed that Frieza destroyed Planet Vegeta, Frieza said it was because the Saiyan's had grown too powerful. Left unchecked the Saiyan's could eventually overthrow Frieza, and he couldn't have that. He set out a plan to not just destroy the planet but also the entire race. The few survivors were told that a meteor was what did it.
Dragon Ball Z: Battle of Gods introduces a new deity to the franchise, the God of Destruction Beerus. In just one line of dialogue, Beerus asks if Frieza had destroyed Planet Vegeta or not. Apparently, Beerus was slighted by King Vegeta and determined that the race should be exterminated. Because of this, Frieza's role as a villain was somewhat diminished since he was doing someone else's bidding. Hopefully Frieza's potential will continue to be explored in Dragon Ball Super.
When Planet Vegeta Was Destroyed
If fans were to watch the available dub of Dragon Ball Super, they would be greeted with an interesting piece of dialogue. Radditz claims that Planet Vegeta was destroyed three years prior to his arrival on Earth. Now this line of dialogue doesn't exist in the manga, but it does create an interesting retcon for American watchers.
The exact date that Planet Vegeta was destroyed and the revelation of how wouldn't be revealed till later in the series There's even a flashback in the anime of Radditz and Goku leaving the planet at the same time. The destruction of the planet and the why of it all would be something that would keep coming around throughout the run of the franchise.
Goku's An Alien
Originally Dragon Ball was meant to be a retelling of the story of the Monkey King, with Goku just being a weird kid who could mysteriously transform into a giant ape. When the series took a more science-fiction turn, Toriyama decided to drop the biggest bombshell the franchise would ever see: Goku was an alien.
Goku's true heritage and his forgotten brother fundamentally changed the franchise. By opening up the fantasy world in a more science-fiction direction, Toriyama was able to tell more varied stories that would continue to build to this day. The franchise constantly works to raise the stakes higher and higher, and it really started with this retcon.
The Demon King Piccolo
One of the best Dragon Ball manga arcs was the Demon King Piccolo. A ruthless and evil demon who sought to rule the entire world. When Goku finally defeated him, he birthed an egg that reincarnated Piccolo into the fighter that Dragon Ball Z fans would know about. Like Goku, however, that wasn't the full truth.
Not only did Toriyama decide that Goku was actually an alien from outer space, but he also decided that Piccolo was. Turns out, Piccolo came to Earth as a young Namekian and completely forgot about being an alien. It was still a little strange when the Namekian were shown to be peaceful farmers but it did create an interesting dichotomy for a while. Piccolo was a ruthless being from a peaceful race and Goku was a peaceful being from a ruthless race.
Bardock Is A Loving Father
Goku's father first gets introduced in the special Bardock: The Father of Goku where he is introduced as a low-class Saiyan who gets cursed with premonitions of the destruction of his entire race. He tries to rally the Saiyans in order to stop Frieza, but he can't, and he is wiped out with the entire planet. Originally Bardock didn't really care for his son, but knew that Goku would one day grow to destroy Frieza.
That is until Dragon Ball Minus where it's revealed that he did love his son and sent him off Planet Vegeta in order to protect him. Bardock would then go to be a major player in the most recent arc of the Dragon Ball Super manga where it was revealed that he was kind-hearted just like his son.
Vegeta's brother
Turns out Goku wasn't the only one with a secret brother. When Radditz showed up for the first time in Dragon Ball Z, it felt like a new and important character had just been introduced, but Radditz hasn't been seen in canon for decades, and probably one of the few Dragon Ball characters who should stay dead. Flash forward to Dragon Ball: The Return of Son Goku and Friends and the same thing happened to Vegeta.
Dragon Ball: The Return of Son Goku and Friends introduces Tarble, Vegeta's younger brother. Most American fans might not be familiar with him because he's never shown up again since this appearance, though he has been mentioned twice. It's frankly weird that Vegeta never mentioned having a brother in all these years but kind of funny that neither Saiyan sibling are very important.
The Reason Why Goku Was Sent To Earth
A flashback scene in Dragon Ball Z reveals that Radditz left Planet Vegeta at the same time as a baby Goku was sent to Earth. That would be later retconned as well, but for many years it was established that Goku was sent to Earth to destroy it. The only reason why he didn't was because he fell on his head as a baby and was raised by Grandpa Gohan.
There has been a lot of talk about how Goku has a similar origin to Superman, but that key difference made it distinct enough, until Dragon Ball Minus and Dragon Ball Super: Broly. Apparently, Goku was sent off Planet Vegeta in order to save him from the impending destruction of his planet. If Bardock was wrong, then he'd go and get him back. This change continues to have major ramifications throughout Dragon Ball Super and makes him closer to Superman than anyone really needed.
The Origins of the Dragon Balls
Once upon a time, the fabled Dragon Balls were powerful objects that could grant any one wish to the person who could find all seven balls. They were created by Earths guardian, Kami to give the people of Earth hope and encourage acts of bravery after King Piccolo's reign. But it turns out they weren't all that special.
Dragon Ball Z revealed that the Dragon Balls of Earth were modeled after the ones on Kami and Piccolo's home planet of Namek. The Namekian Dragon Balls were more powerful than the Earth ones, but Dragon Ball Super introduced even more powerful ones. Apparently the Namekian Dragon Balls were created from shaving off pieces of the Super Dragon Balls. The franchise gets a with so many Dragon Balls because it's in the name, but it's getting a little ridiculous how unimportant these things are.