The team already completed an A rank mission by accident.
They also completed a B rank mission already, during the attack on Konoha (I think it was to catch up to Sasuke or stop Gaara or something).

Originally posted by: 010577
Is this supposed to be a mistake that the filler is doing?


tsunade ranks the mission at least a b...

when 3rd explains that genins do d to c
chuunins do c to b
jounin to b to a


either the filler made a mistake or naruto is a chuunin if logic needs to be explained


zabuza saga was supposed to be a c