It is tough to tell what is going on...with live rock and live sand, you might avoid big spikes and it could have only taken a couple weeks...but did you ever get any ammonia and nitrite readings? I agree that the low nitrates seems odd.
Ideally, to be sure you are cycled, you could add pure ammonia to about 3-4 ppm
and see how quickly it drops to zero. If it is cycled properly , it should be back to zero within a day (24 hrs). That shows you have sufficient beneficial bacteria to handle the ammonia produced with fish waste.