I don't understand Sephiroth *spoilers for a 30 year old game*

(I just played 7 and Crisis Core for the first time.)

So he knows SOLDIERs are made through experiments, and he knows this can lead to some people turning into monsters, and knows Project Jenova is a thing, yet just assumes it's a coincidence it has the same name as his "mother," apparently knows mad scientist Hojo is his father, and he has fucking cat eyes and abnormal abilities...but somehow doesn't piece things together until he's like 30 years old when he gets told to go to a [not even secret] Shinra facility that has JENOVA slapped onto it in giant letters and Zack asks him like the first obvious question you would ask in that situation.

Am I forgetting and Sephiroth didn't actually know about Project Jenova? If so, why would they even send him to Nibelheim if it was supposed to be a secret? And if he did know, why didn't he ever piece this stuff together himself, esp after all the other shady shit that Shinra had already been up to, including Project G with his two best friends?

Like, his break down just seemed random every time I rewatch it, cuz like...this shit should've been obvious if he had thought about it once.

Probably the straw that broke the camel's back moment.

Like "I've been always suspicious, but now i have the evidence it's true! No more pretending to be good boy, I'll go mad and wreak havock hahahaha!"