Every Thai meal should be accompanied with a standard set of four condiments on the table: sugar, dried red chiles, fish sauce, and fish sauce with sliced chiles in it. In Thailand you're as likely to see all of those on your table as you would find ketchup at a burger place here.
So, what Thai restaurants in DFW either have them on the table as a default or will bring them if you ask? I'm using this as a not-so-reliable barometer of authenticity.
Andaman in Denton will bring you dried chilies, fresh chilies in fish sauce and I believe the dried chilies in oil. They will also bring any fresh chilies or sugar if requested. I haven't ever asked for fish sauce as I hardly use it in any dishes. All the dishes I have had have been to my requested spice/salt level or have brought the requested fresh chilies.
I am pretty sure Bambu in Richardson, Thai Chili in Carollton and Jasmine in Plano (Alma and Spring Creek)will do the same.
Most places wil usually put soy sauce on the table in place of fish sauce since that is what most customers ask for. I believe demand over keeping authenticity is what determines what is on the table.