Well, I asked my mother who spent some time in Mexico in her youth (and I mean real Mexico, not TJ). According to her, HARD tacos are an invention of fairly recent origin and likely by an American. She said that she remembers pretty much stuff was just thrown into a non-cooked tortilla and was called a taco. She didn't remember the difference about a burrito, but thought it was likely the folding.

I intend to ask a friend of mine who does mission work down there regularly when I see him tomorrow (called him just now but he wasn't home). Being in SoCal and roughly an hour away from the border, I intend to get to the bottom of this...

Stephen