Folk traditions often - indeed typically - have multiple creation stories for various aspects of nature. These etiological legends, as folklorists call them, were part of the "welling up" of folk of explanations. It is unclear whether a single culture came up with alternative stories or if diffusion brought multiple legends to a single people.

In the storytelling setting, folklorists have observed people telling a legend to explain the existence of something like the sun. When that person finished, another was apt to say, "Yes, I have heard that, but I have also heard that ..." And then there might be another - or several others, and people discussed these various possibilities, but there wasn't necessarily an attempt to reconcile the contradictions. Perhaps one or another person would personally prefer to embrace just one of those explanations, but mostly folklorists observe people in pre-literate cultures able to deal with these diverse legends without a clear answer to the question you pose.

In short, your question is a problem for modern people looking back; it was not necessarily a problem for pre-contact Aztec people. Most importantly, there was no single, "true" story. They stand next to one another in equal co-existence.

To piggyback off of OP's question and to make it a bit more of a less flawed question, per /u/itsallfolklore 's point: What are the origins (or, rather, what is the origin of our knowledge of them) of each variant of the 5 suns myth, and how do they compare and contrast? Was their presence in Nahua societies separated temporally (IE, the myths evolved from one version to the other over time) or geographically (IE, different altepetl believed different ones)? How does each variant play into and related to Tlacaelel's reforms of Mexica religion in particular?