Those mythical other biological processes aren't releasing 2.3 dKH. They have already fixed out the carbonate and it's not available. Want to set to set up a bunch of tanks, add ammonia, and see where alk ultimately ends up? Put money on it?
Also, NO3 doesn't directly convert to nitrogen gas. This requires anoxic layers which cannot under any realistic scenario fixate nitrate to an equilibrum in a closed loop reef tank.
There are a couple of incorrect statements here. It is very true that if you set up a new tank, with new (dry) rock, new (dry) sand, and other equipment that has been out of the water for a long time, there's no significant nitrifying bacteria present. If you then add ammonia, the nitrosomonas (and others) that are always present in the environment will innoculate the tank, and start growing and consuming the ammonia that you've added. That absolutely will consume alkalinity, though whether you can measure the effect or not will depend on the amount of ammonia you've added and the precision of your alkalinity assay.
Later on, and presuming that you have significant porous rock and/or sand in the tank, nitrobacter bacteria will start to populate the anoxic zones in those substrates (there are always anoxic zones in any porous substance in an aqueous environment, presuming those substrates have individual units that are big enough to see). Those nitrobacter populations will definitely start consuming nitrate and yielding alkalinity back to the water, and nitrogen gas that escapes to the atmosphere.
The net behavior of these two bacterial populations is that at some point (and it may take many weeks of "maturing") is that the nitrate concentration will reach a steady state in the water, presuming that nitrogen is being added in the form of biological substances containing it (i.e., food). The aquarist will observe a net increase in nitrate concentration and a net decrease in alkalinity at first, and eventually, a net decrease in nitrate and a net increase in alkalinity.
Denitrification happens in
every reef tank, again presuming that it has porous rock and sand. Whether or not it happens to a significant extent to stabilize nitrate concentrations at relatively low levels depends on many factors, including the availability of a carbon source. That, by the way, is one of the reasons that carbon dosing is effective at controlling nitrate in a reef tank.
. In another case, it is a challenge to all participants in the discussion, because everyone defends their point of view and experience, confirming their reefs.
