FF7 plot question, Sephiroth/Jenova related (SPOILERS)

[MaslowK]

So this has been bugging me for a while and I still don't understand it entirely. It's revealed later on in the game that Sephiroth is actually in a big block of mako at the north crater. This raises some questions; who the hell was it that Cloud talked to in the shinra mansion basement, who was that on the junon ship, etc. I was just watching a retrospective on the FF7 franchise, and apparently the idea is that these apparitions are actually just parts of Jenova shape-shifted into Sephiroths form and controlled by the Sephiroth at the crater.

This is all fine and good, but that raises the question of how Jenova escaped from the shinra building in the first place. Is there something I'm missing here, or are we supposed to just assume Jenova simply chose not to escape until it was told to by Sephiroth?

[Aeolus Aeneas]

Yes, the "Sephiroth" you're chasing all that time is simply Jenova, or rather, by the end of it the head of Jenova that Sephy cut off back before Cloud threw him into the Lifestream in his hometown reactor. It showed up in the ShinRa building, I assume, to get its body, which it then used as parts to fight you. Jenova BIRTH, I believe, was an arm. As to why it picked the moment Cloud and his band of morons were in the building? No clue. Maybe to help start the Reunion. Maybe it felt Aerith and wanted to check out the last Cetra and her child bearing hips. Maybe it was pulled in by the gravity of Tifa's breasts. Maybe Cloud used MIND POWER to summon it for lulz.

Maybe the story is a pile of crap and they didn't think that far ahead because it seems FF7 was thrown together in less than a year, which is why it's a mess.

[MaslowK]

by the end of it the head of Jenova that Sephy cut off back before Cloud threw him into the Lifestream in his hometown reactor. It showed up in the ShinRa building, I assume, to get its body

OH, well see now it makes more sense. I was more confused as to how the Jenova in the shinra building managed to escape on its own than why it chose to do it when it did, but if part of it was already loose that would explain that. Thanks!