Here's a curious li'l retcon that most people don't seem to know about.Most people rightfully assume that the Androids that Trunks warns Goku against are No 17 and 18. I mean, it only makes sense, right? It's the reason why Trunks reacts the way that it does when he sees 19's head on the ground.
Actually…
"But wait… this is an error with the translation, right? It makes no sense otherwise. And it's not like even an official translation can't get things wrong sometimes." Actually…
Yeah. Trunks actually calls Android 19 and 20 out by number in the manga, then comes back to the past, and the narrative acts like he never said that.
Curiously enough, this was a detail that was not only in the original publication of the manga, but also its reprints. Toriyama hasn't exactly been shy about changing details on the fly before to suit the story he wants to tell, so why this particular detail would remain even in reprints is beyond me.
One example that immediately springs to mind is the age of Son Gohan. In the original printings, he's introduced as three… but in the very next chapter, Gohan introduces himself to the audience before the story starts, and states that he's four.
And the reprints for that reflect that change.
See? You can even still see him holding up three fingers.
See? You can even still see him holding up three fingers.
Going back to No. 19 & 20 situation: The anime sidesteps this entirely by only calling them by them "the Androids"—or "Jinzōningen" for the Japanese script. (I listened carefully to see if I could hear Trunks speak their designated numbers, but he doesn't seem to.)
If you never bothered reading the manga, it isn't a detail that you'd catch… and to say that far, far more people are familiar with the anime would be a massive understatement. So, it's understandable that this would be a detail that most people wouldn't know of.