The question was asked about whether "Kentucky Straight Bourbon Whiskey" can be a combination (we dare not say "blend") of straight bourbons from different distilleries. The answer is "yes." Somewhat obviously, to be called Kentucky Straight Bourbon Whiskey, all of the whiskey must be straight bourbon made in Kentucky, but it can be made at any Kentucky distillery. In fact, even if the word "Kentucky" were not used, all of the whiskies still would have to be from the same state, although they could be from any distilleries in that state.
The question was asked in reference to Corner Creek and although I don't know where Corner Creek's whiskey comes from, and I am a little skeptical about their claim that they are mixing rye-flavored bourbon and wheated bourbon, it is possible, for purposes of this explanation, that they are using wheated bourbon made by United at Bernheim and rye bourbon made at Heaven Hill's Bardstown distillery. They can do that and still call it "Kentucky Straight Bourbon Whiskey."
This is not a common practice (mixing straight whiskies from different distilleries). A much more common practice is mixing whiskies from the same distillery but different seasons, i.e., improving some 4-year-old by adding a barrel or two of 8-year-old.
To be assured that you are drinking the product of a single distillery made during one distillation season, you need to buy either a single barrel product or a bonded product.
As for some of the categories we seldom see, a blended whiskey containing not less than 51 percent on a proof gallon basis of one of the types of straight whiskey can use the name of that specific type of straight whiskey; for example, "blended rye whiskey" (or "rye whiskey--a blend"). This is, however, still a blend and can contain green whiskey, high proof (above 160) aged whiskey, or GNS, as well as colorings and flavorings.
The term "a blend of straight bourbon whiskies" would describe a mixture of all straight bourbons that does not conform to the definition of "straight bourbon whiskey" which, presumably, would mean a combination of straight bourbons from different states. As I read the regs, this is the only time the word "blend" is used to describe a combination that is actually 100 percent straight whiskey, so this term is an oddball. Usually if the word "blend" appears in any construction you are talking about a product that contains green whiskey, high proof (above 160) aged whiskey, or GNS.
Why state of origin is important I can't explain, but note that these terms are seldom used so their application as a practical matter probably has never been fully explored.