Irwin actually brought over the SBC/AB toys figures all in one shot before the dub had gotten to Cell saga in the US. from 98 through 2000, they did 13 series of figures, which included a lot of characters not seen one US tv yet, including Vegetto, Cell, various SS forms, and Buu, who hadn't even had his name officially localized so he was "Boo". As for why they did this? Maybe they expected it to sell to older fans who were already familiar with the series through fansubs.
Around the end of this line, Irwin would make an original, more concentrated, non-gimmick line of figures that followed alongside the US release of the series. Saiyan/Frieza saga stuff in 2000, Androids/Cell in 2001, Buu saga stuff in 2002.