In Dragonball Z, the Saiyans send baby Goku to Earth moments before Frieza destroys the planet Vegeta. Although the movie Bardock, father of Goku is a movie and should exist in the movieverse, it is official canon for the show as well. At the start of DBZ, Raditz tells Goku that the planet Vegeta was destroyed three(3) years ago, yet Goku is in his mid 20's when Raditz arrives. How could Vegeta have been destroyed only three years ago when Frieza destroys it right after Goku is sent off planet? Is this just a continuity error?
Dragonball is an anime based on a manga source that was still being written as the show aired. The definitive source is the manga or works with writing credit given to Toriyama. (the creator of the series)
Bardock: The Father of Goku has such a writing credit.
Additionally the show corrects itself when the relevant time period occurs. Likely the 3 years figure was just written in by mistake. Normally we try to twist ourselves around on this site to make mistakes still somehow make sense, but this goof is really just the product of some writer not knowing what the future would hold.
Dragonball, and any anime based on a yet-to-be-completed Manga really, is full of little inconsistencies like this. Here is a list of many of them.