I don't think we can compare it to the schools and tests we went through.
I think you can graduate if you fullfill the requirements.
Just like the drivers license. You need to know the theoretical part. If you think you know all the answers you can probably take the test (and if the teacher thinks you can). So it's not like going to school, which requires several years.
Next there is the practical part. Like they needed to do a Bunshin in the exam or the henge jutsu before in class.
If you can do it and know all the theoretical stuff you can graduate. No need to wait several years, is there.
If you know all the shinbi teachings and guidelines and you have control over your chakra you graduate, if not....
Also. The Bunshin exam was the last requirement in the exam. After doing that all the others graduated.
We can assume they all passed the other test before that. Either it was in the same test (an overall test) or they passed them days, weeks or months before the last test.
Naruto passed the other test. Otherwise there wouldn't be a need to let him take the final exam.
He didn't graduate because he couldn't do a proper bunshin.
Do you think they would make him spend another year in school because he couldn't do a bunshin.
If you fail you can probably take the test again shortly after you failed. Just like in driving school.
Sure, there are still some unknown things about how it works.
But i bet Kishi didn't screw up somethink like "oh naruto is actually 3 years older"
If you believe that, the only thing you can do is Harakiri, for doubting Kishi
"For Feanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strength and subtlety alike, of all the Children of Illuvatar, and a bright flame was in him"