Most people should know if they are 3Q. If you weren't, you'd probably know. The 3Q's are:
1. Physically: CFA test. You know if you couldn't do something or you bombed it.
2. Medically: If you weren't medically qualified, it would say so on your application.
3. Academically: That one is tricky. 3.2gpa and 25ACT is "Qualified", but chances of an appointment; (Unless you got a principal nomination or there were NO OTHER NOMINEES on your MOC's slate); are really slim. So that's the only one that's possibly vague.
The thing about this however is: "Normally", you can't become a "Candidate" unless you are qualified across the board; OR you receive a nomination. So, if you received a presidential nomination because your mom/dad is retired military; but you have a 1.3gpa, you'd be listed as a "Candidate" because you have a nomination, but you wouldn't qualified. Also, you could have a MOC nomination making you a Candidate, but didn't take the DODMRB physical or CFA yet, so you might not be qualified.
But under NORMAL circumstance, if you were classified as "CANDIDATE" PRIOR to getting your nomination..... then you KNOW FOR A FACT that you are qualified. Because the only way to become a candidate is to be 3Q Qualified. (Or you received a nomination). But most MOCs won't give a nomination if you suck academically. DODMRB will say on the application if you aren't qualified. And you know if you didn't pass the CFA. Hope this explains it.