It makes me very sad but unfortunately Hasbro does not have any obligation to maintain a consistent backstory really on anything. The journal of the two sisters and the other books and the comics occasionally have the same lore but not always and it is rather frustrating. The show seems to impact the comics but the comics don't impact the show and they don't even consider any of the original books or movies from like the 80's I think. According to the Journal of the Two Sisters (which I think every pony should read) alicorns were a race separate from the others and the other races knew about alicorns, but not a whole lot... StarSwirl the Bearded would actually be the only character to have reliable consistent knowledge of the situation because Celestia and Luna were very young when they became the guardians of Equestria. I would love to see Lauren Faust and the other writers come together to make a StarSwirl journal or even better yet, a History of Pre Equestria. I would die. Think about it, even Celestia thought Zebras were a legend atone point XD so there is a lot left unknown about the history of the races. They asked the alicorns the eco e leaders because they shared attributes with all the races. Even though they were separate. And just because two species look the sa,e it does not mean they are as closely evolutionarily related as one may think. Just saying.
Side notes: alicorns are always associated with royalty (mostly) but before Celestia and Luna were asked to be the Princesses/guardians each race and region had their own leaders. Yet for some reason the alicorns educated their young with the Royal Canterlot voice (how Luna refers to herself as We), which is interesting. And then there is somehow Cadence, when the hay did she come from???? She was an alicorn and princess in high school??? Princess of what???? And she is a distant relative of the original ruler of the crystal empire, Princess Amore, who was a simple unicorn. Can someone explain that one, please. I stand by my previous assertion (somewhere among the forums) that their society is loosely following the Greco-Roman model in a matriarchal way.
Super side note...where did umbra ponies come from and go and why are they trapped in crystals, and where did changelings come from.....