it's been a process of discoveries since day one, if not since before
self awareness is kind of a spectrum
We know we had some kind of self awareness during infancy when one of our eldest beheld the chaos of the world around us and thought, "Not this again, I hate this." Probably realizing for the first time that moment of waking awareness (day) was like the last one.
We remember learning "mom" and "dad" while lying in the crib and being picked up by our parents. And we remember recognizing the repetition of those experiences and what they felt like. The differences of being held by mom and being held by dad.
But, then, much later, at something like six years old, we once received a birthday gift that we didn't like and we screamed and cried about it, intimately aware of our own feelings about it and how we felt hurt, but not aware of how our reaction impacted our friend. It would take a while to learn that lesson.
Also, being plural, and always growing, we are full of new people still learning these things. We help each other out as best we can, but it's a continual process. Learning that we were plural in the first place, and gaining selves awareness, took so long that we didn't accept it until we were 41 years old.
Interestingly, when you're plural, it's possible sometimes to share your awareness of each other, and in so doing be more self aware than anybody else can possibly be. While also being impaired about it through dissociation, amnesia, and the stubborn bullheadedness of your headmates.
And, through all of this, we have never held or accepted the idea that we are human. All evidence has proven otherwise.