Since civilizations prior to widespread literacy (and many after it) routinely destroyed the records and lore of their rivals; we should expect that the first X that we have records of is quite certainly not the first X that existed, especially if its lore makes a big deal of claiming that it is.

This would work if conquerers were also effective at destroying archeological evidence. But they seem not to have been, and a complete archeological record would just settle the question of which city was really first, given some appropriate and agreed upon standard. And that city would be the true dawn.