User blog comment:Salubri/Hollow. Arrancar, Espada & Vasto Lorde/@comment-1454424-20100818184628

Grimmjow is no. 12 because he was turned into an Arrancar after Shawlong. The fact that he is no. 12 and Shawlong is no. 11 doesn't mean anything other then the fact that Grimmjow was "born" after Shawlong.