Are there any sources for authentic versions of traditional dishes? For instance I believe that the version of Guacamole that I prepare is not traditional because of the use of coriander and lime so is there any where I can look up a tradiational version of the recipe so I can compare my version with the traditional version.   I know that even traditional recipes will vary somewhat with regional and family variations but I would have thought that there are enough elements of commonality that I could tell how my version differs.  
Authentic is a myth and a moving target.  Bless your food with delicious instead.   Cooking is using what's around and tastes good.  All cuisines evolve.    If you want to approximate traditional dishes, consult a nutritional anthropology text or a culinary historian (they exist, really).  More practically, ask a Mexican. (Or a Swede. Or a Brit... Per the cuisine). Preferably one who lived there. Better one who cooked there. Ideally one whose grandma cooked there.   Also, a "customary" recipe sounds like one you'd find in a tourist-shop that sells regional cookbooks.  They might not be up to the standards of modern regional cuisines, but the whole "modern" part probably means it's not "authentic" anyway.   