These are sources of phosphate in a tank which is not being fed, especially when new. Plasitcisers are often phosphate based, and when added to the tank can be a significant source until the residue has been used. Your right that food is a major source of phosphate in tanks, one which is unavaoidable, so you need mechanisms in place to deal with leftovers and th eventual waste.
Huh because it's a wierd question. What's unknown about the system? (Also, I'm not, and never have used it.)
Vodka (an other small organic molecules like acetate) feeds bacteria, which are literally everywhere in the tank. They are the ones which are responsible for storing and releasing differing forms of phosphorous. Bacteria consume phosphourous in much larger quantities than they need to live and reproduce, so inducing a bloom will suck many different forms of phosphorous, not just the water soluble orthophosphate. This is where it differs from rowa and stuff like that. For oxide removers to work, they need water soluble forms of phosphate (mainly ortho, but also some organically bound stuff as well). These forms only exist when all other pools (including bacteria) are full.
Vodka isn't any more "unkown" than rowa and other resins.
Phosphate problems come from the simple fact that there is more phosphate going in, than is been taken out.