User blog comment:Gary299/High School DxD BorN episode 4 review/@comment-73.178.133.185-20150427011001/@comment-1359322-20150427063449

I wonder how many times have i said to you Otaku. They are doing it to expand Rossweisse and Irina's role, not because the budget. If they animate only 5 & 6, then both Rossweisse and Irina would appear for less than 1 episode for the total season in entirely (Rose only appeared for a short while in Volume 5 & Irina only had like her school entrace and the Juggernaut Drive section. So it'd be like having no presence at all over the span of 12 episodes. Unless if you're happy with seeing the 2 of them for only once or twice this season.

So they added Volume 7 which the two also appeared in but like Volume 5 & 6, Volume 7 barely focused on them as well. So they changed the sequence and change it in a way that Rose and Irina are more relevant to the plot.