A narrative of human action becomes legend when perceived to be true by both teller and listener. It is not invented or made up. It exists within the likelihood of fact and is believed to be true because it took place within the realm of possibility in human history.

Cowboy legend is the culmination of tales recounted by those who
were there, told from varied perspectives, perhaps distorted by
perception or embellishment, but verified as true by collective recall.

Legend is where truth and folklore combine to become, by all
intents and purposes, something very real.

Herein are the elements of our history, mostly fact, some
partly exagerated, perhaps a few invented all forming the
Legend of the Cowboys