User blog comment:DeathGodPrayer/Talk About What You Want!/@comment-162.202.198.72-20130913051446/@comment-5185939-20130913063508

It's been stated that Issei is on the level of a High Rank Devil, the only thing keeping Sirzechs and the other Maoh from giving him the recommendation is the fact that letting him rank up that fast will cause some problems with some of the other noble families, so they're letting him run around as a Mid-Class for a few months.

I wouldn't be surprised if, life permitting, the Gremory will have Issei trained up well enough to pass the exam by the time things have calmed down enough to let Issei take the exam.