I knew that years ago because Toriyama mentioned it in one of the blogs at the beginning of the manga volumes. A fan noticed it and wrote to him, he said "blasphemy!" but then realized it was true.Rory wrote:Yajirobe appears on the spine of the Tankobon... twice.
Another thing I noticed was that Kaiosama on the spine pic is holding the Arale shit pile on a stick.
Something that I didn't notice until recently: Everything in West City or is associated with Bulma is in English, this explains the English naming scheme of Vegeta's attacks after he moves in with Bulma.