I have written to them, too! They haven't answered me yet, but I am expecting very much this answer.
(For me, this is another reason, along with what I consider to be a questionable protein source & some overly "precious" customer service attitudes, for not buying certain brands of feed that already have NutriBalancer mixed in. What I do is stir NutriBalancer into my daily serving of Fermented Feed just before the feed bucket heads out to the coop. I'm using a bit less than the full 3%, and I offer calcium on the side. I started doing this at the same time I started fermenting some of their feed because my already-rough-looking flock went into a simultaneous and hideous molt ... and boy is my flock looking and ACTING so much better now! SO much better!)
As I stated before, I believe this is due to the way water soluble vitamins lose potency when exposed to moisture. For example, if you grind up a niacin pill to add to drinking water for ducks, then the water will have to be changed at least every 24 hours, and new niacin ground up & dissolved into it, to keep the potency of the niacin close to adequate. You even have to ingest water soluble vitamins "every day" to keep enough of them in your system because your body flushes them out ...
This is why it is so much harder to overdose on water soluble vitamins.
BK has made a very good point, several times, about the increased nutrition of properly fermented feeds ... about how much the niacin (specifically) is increased in properly fermented corn ... so presuming we are fermenting our feeds properly, then there is less need for (at least some) supplements. If I hadn't been in such a panic about the state of the flock, I would have started with Fermented Feed first, and then added supplements if I didn't feel the birds responded well enough with "just" that.
I think this is a very interesting facet of the discussion of fermented feeds ... how to best use our ingredients to get the most nutritious results for the birds.