There's two possibilities for cybertronians. Either they know where they come from, in which case there's no mystery, it's just a fact they understand.
Or they don't know where they come from, and as such they, being very human like in intelligence, would obviously build belief systems to explain the world around them.
That's why I prefer the 13 to be mythological: legends ancient cybertronians shared to explain things they don't understand, like where they come from or what causes natural disasters. Over time the disparit stories and figures are brought together into a global pantheon, ala the Olympian gods.
I'd love a "Tales of the 13" book that was just a collection of various mythological stories "taken from cybertron." The "Covanent of Primus" is too much "Alpha Trion's blog" to feel mythological. (Also the quality of the writing leaves a bit to be desired.)
Though, like Primus, nothing can be a belief for Transformers; their gods and religion have to be demonstrably real, so I don't expect anything like this to happen.