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My Aunt was a supervisor at a blending/bottling plant in the San Mateo area that bottled most of the alcoholic beverages sold in northern California.
She used to spill the beans to us on which ones were real, and which were blended at her plant.
There is very little out there that is real.
There is some difference in the quality of the alcohol used for blending though.
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Depends on what you mean by "real". If the end purpose is maintain consistency of taste, of course that stuff is blended, grape quality and taste varying year by year.
As for the alcohol, I hadn't thought about that. Just from the taste variances in vodka alone, I guess that would make a big difference.
Why use 190proof corn alcohol (what Heinz uses to make their white vinegar) when there are probably lakes (to use a EU wine policy term) of really bad and undrinkable wine to fractionally distill once, and use as the fortification boost/base?