User blog comment:Dxrd/Fixing "Dragon Ball Z: The Dead Zone" (July 15th, 1989; 45 Minutes)/@comment-3097771-20190412235114/@comment-1815410-20190413143745

Piccolo and Goku stated that they've never thought they'll have to join forces upon fighting Raditz.

Gohan needed to have faced Garlic Jr. before Raditz and the Saiyan Saga in order to allow the Makayan into the franchise's timeline, and Goku must've obtained the Dragon Balls within a year since they need to be turned into stones after a wish was granted so it's best if the movie's story was one year (and a few months) prior to Raditz's arrival.

Still "personal opinion"?