The grapes should ALL be from the same Douro region, I don't think you'll get much more information than that. My criticism towards Portugal's lack of export savviness is more to the fact that all brands I see abroad are typically non-Portuguese (Whereas you have to assume the vineyard belongs to a foreigner/company). Brands like Ferreira, Velhotes, etc are not commonly seen outside Portugal, on the other hand, common international brands are not typically consumed by the average person (lack of knowledge of said brands + higher price probably drives the Portuguese away)