In some states, like Texas, in order to sell a spirit as your own, you have to "rectify" it, even if you TIB it in. There is some dispute over exactly what "rectifiying" means to Texas, but I've usually understood it to mean that if you buy 190 proof GNS, you can't just add water to it to bottle it, you have to run it through a still at least once to pass muster. I believe this is how a certain large litigous Texas vodka maker does it. How this applies to aged product purchases is what is in dispute, but you can see that this requirement would trump the new TTB reg by actually distilling the product.