Why does summon monster 7 allow you to summon a CR 9 monster (avoral guardinal) and summon monster 9 allow you to summon a CR 8 monster (the couatl). Is this just an error or is there a reason?
That said, I do not think Summon Monster strictly follows CR's. Some creatures could be valued higher than others if they have special abilities that could be of use outside combat, like the Couatl's ability to use Plane Shift at will.
