Board Thread:Naruto Discussions/@comment-7292165-20140715160041/@comment-1744929-20140716154329

In the manga it was clear that the Bijuus had to be collected by their tail numbers, starting from 1 and end it with 9.

Yeah, I know it has been changed later like everything else, but that was the original case. Also, the anime is not cannon anymore thanks to mixing fillers with the original story directly and changes things. For example, the Slug Bijuu was captured in the manga already, but in the anime it came later.