A few episodes into the relaunched Dragon Ball Super, fans complained of a noticeable drop in animation quality. What was intially a fine-looking anime suddenly became something like a school project belonging to a kid who should probably give up their dream. Thing is, Dragon Ball has pretty much always been inconsistent in the visuals department. Above on the left, you can see a pretty decent Goku in episode 168, and to the right is a derpified version from the very next episode.
Kanzenshuu has a great article chronicling where and how this sort of thing happens. Basically, because of budget and time constraints (and a variety of other factors), different episodes get handed off to different teams. It's a common practice even for American cartoons like Tiny Toons. No animator is created equal, and as a result there are sometimes vast discrepancies from chapter to chapter. Even episodes that depict the exact same scene can be as different as an apple and the bruised reject apple in the produce section that everyone puts back down.
There are "Character Bibles" to be sure, but these guides don't guarantee a congruent look between episodes. You might not have noticed it back then, but there's a big difference between "epic flowing hair Vegeta" (bottom right) and "clearly has a cocaine problem Vegeta" (top right):
This is just the kind of thing you have to deal with when you run into such a long-running series. Sometimes, sacrifices in quality are made in the name of quantity. The best thing that can be said for DBZ's animation consistency is that it gives you an extra appreciation for the truly beautiful episodes.
Changes are inevitable when you're translating from the page to the screen, but Dragon Ball is kind of a special case. Toriyama was drawing new chapters of the series constantly, while the anime was running at the same time. And they never pulled a Game of Thrones and jumped ahead of the books, but instead came up with ways to expand or extend the story -- which is how "Five minutes until Namek explodes!" became a six hour miniseries.
The need for padding gave us superfluous storylines that weren't in the manga, like the frogged Captain Ginyu temporarily swapping places with Bulma.
A lot of these "filler" episodes were inconsequential trash, but every once in a while the B-team hit gold. The episode where Goku and Piccolo get their driver's licenses has absolutely no bearing on the rest of the series, but it's still pretty awesome.
Most of what was in the comic did end up making it to the show, simply because the animators wanted to use every inch of the manga that they could. But sometimes the violence was a little too extreme, even for a show where people try to kill each other every episode. There's a particularly brutal scene early in the Android saga that didn't make it into the anime. When Dr. Gero first appears, he stops traffic and then... well, just look. Remember, read right to left.
Holy shit! Gero just straight up squeezes that guy's head off at the neck, like the world's most twisted balloon animal artist. This is an unprecedented level of graphic violence that is never approached in the anime, even when Gero impales Yamcha with his bare hand.
Of course, where there's wanton violence, gratiutous nudity is sure to follow.
There are panty shots and teases in the show, but it never really goes "all the way." The manga, however, wasn't afraid to exploit its token female at any given opportunity. Bulma is partially naked in several scenes like the one above, which are obscured or altered altogether in the anime.
Some of the changes are a bit more subtle, but last for the entire series.
Look closely and you can see that in the manga (left), Piccolo only has four fingers total, but in the show (right), he has five fingers. It's kind of a baffling change, one that makes you wonder whether animators drew Piccolo with a full set of digits by mistake and kept rolling with it after they realized their error.
That would be a plausible explanation, if it weren't for how Cell turned out.
In the manga, Imperfect Cell has three-fingers on each of his Ninja Turtley hands, but they revert to the five-digit standard in the anime.
Even Majin Buu didn't come out of the adaptation unscathed.
As you can see, Buu has these gooey mitten hands in the source material, but is given human hands with stylish black nail polish in the show. We can probably guess these finger changes are for simplicity's sake -- with several animation studios working on different episodes of the show at any given time, it's probably easier to avoid confusion and possible inconsistencies by just giving everyone the same hands.
In the end, that's not a big deal. Unlike this:
There's no way that can be right! CAAAN IIIT!? Indeed, the famous "Over 9,000!!" meme should really be "Over 8,000!!" That's what it read as in the original manga and Japanese version of the anime. Some suspect that a mistranslation was to blame, or perhaps the localization team just thought that 9,000 was a better lipsync match for the dub. When they were remastering and re-editing the series for Dragon Ball Z Kai, they actually changed the line back to 8,000. But in our hearts, we know what the scouter really says about Goku's power level.