> People are always taken back about how much classic staples didn't exist prior to the discovery of America.

> Yet we talk about 'authentic' cuisine we usually use it in context way before 'America'.

I can pretty much guarantee that's not true of discussion of authentic cuisine of the Mexican or Tex-Mex varieties, since “Mexico” and “Texas” are both post-Millenial identities, and both identities of the Americas. Sure, it might apply to some views of authenticity of European, Asian, or African cuisines (and if by “America” you actually mean the “European colonization of America”, which some parts of your comment suggest, it might apply to similar views of authenticity of Native American, including Inuit, Aztec, Inca, etc. cuisine.

But, even where it might apply, I don't think that is what people usually mean by authenticity; they mostly mean before changes made to support mass commercial distribution or production, and without adaptation to ingredients they are locally cheaper or more popular in places outside of the place where the cuisine originates. (In America, that concern might often be phrased as “before Americanization”, but that's not “before any impacts of the discovery of America”.)