The reason that it can't be labeled as a straight bourbon is that there's a non-bourbon component whiskey. It also can't be a blend of straight whiskies as they all need to be of the same type (though this wasn't your claim).
So, to be clear, are you saying that you can mix any of your other whiskies with distillate from a bourbon mash and, as long as you only put a little in, you can still call it bourbon and not bourbon with xxxxxxx like Red Stag and the others?
85% high corn bourbon and 15% quinoa whiskey = bourbon?
85% high corn bourbon and 15% smoked straight wheat = bourbon?
85% high corn bourbon and 15% ryemageddon = bourbon?
I've understood the use of the term "four grain" in bourbon parlance as either a bourbon mash with two flavor grains or a marriage of a wheated bourbon and a rye bourbon. You're using the term to describe a bourbon mash (of what I assume is ryed) combined with a straight wheat whiskey to attain the 4 grains. Is this correct?
I still believe that the product is mislabeled as a bourbon and I hope the TTB can address it, regardless of the number of bottles in the run. Honestly, I find the "it's just a small run, regardless" attitude to be dangerous. More water in my bourbon is not what I'm looking for, and watering down the bourbon class type can only lead to more strangeness down the road.