With PCa there are always exceptions and with thus so with even the psa test (by itself it is not all the accurate or useful), there are a few rarer or aggressive forms of PCa (18 variants exist-search internet). These rarer types (a few of them only) don't give off psa's to measure. So yes you could be among the very few that show a normal or even very low psa and yet have very aggressive PCa or even alot of it in some rare cases, it is not the average case or norm in this arena.
What is important about psa for the masses of patients (i.e. most presentations of PCa people), is psa history (yours over time) and psa velocity, how fast did or does it increase-double-triple and such. Those are useful as "red flag" prognosticators for further tests or biopsies and could lead to needed treatment(s). If your psa ever doubles in a one year time, does not automatically mean PCa, it does mean you need further testings (asap), unless you believe in a darn the torpedos mentality, you should seek methods to find the why of it: could even be other causes like prostatitis (an infection), etc.
The fact about PCa is there is no definitive answers that fit everyone or every scenario, exceptions, exclusions, insanity exists with this at every measurement or method or testings. If you do not realize this, at some juncture you will and some docs might be frank enough to give it to you straight and even admit the profits off the drugs and rush to get some patients into a treatment does exist, along with bias and agendas. (it has been called a cottage industry in the media, for real reasons). Some patients need treatments (asap), some others do not and have more options than they are lead to believe. It is very difficult for even pathologists to render the decision on which variant of PCa does one have: thus there are '*****cats' versions (non-aggressive not very threatenting presentations) and then there are 'aggressive' versions that are very tough to fight, the urologist has no clue which type you have....the pathologist might be able to distinguish which you have. This is one of the biggest problems with defining what a patient is facing and has to fight. Proper assessment, staging, and all these variables are lacking and thus you see the variations in patients responses and results. It is the land of bizzaro, land of limbo, twilight zone and jungle all in one, a machette might help one cut away the b.s. and see it more clearly.