I doubt it is saved, because next cmdr can also generate it on the fly as his/her game will also follow the same procedural generation rules
Im pretty sure the system IS saved once it's visited, because if it weren't we would expect to see variations in the procedural generation between two commanders, but we dont. You can tell a commander what is at system Z and if they go there, they will see the same thing. Also, there would be no way of storing "first discovered" tags if its not saved.
lets say someone is traveling to system -PDQ 1. An undiscovered M class red dwarf planet somewhere coreward of Sol.
The CMDR hits the jump button and the system goes to work:
"is it a known system? no, ok generate it"
"its an M class red dwarf that means it has this much gravity, this is whats around it, its coreward so it will be X Y and Z, that allows for planet types A B and C, throw in some random generation, we get an M class red dwarf with two planet A's three planet B's and one C at the outside, lets roll some procedural textures based on atmosphere, ok done." It then saves this generated system to a database.
It does all this during witchspace, you drop in to the sector, honk, and see stuff.
You scan stuff and then go back home.If it didnt save the system when you visited it CERTAINLY does at this poin that you sell the data. This may be one reason selling data takes so long, its updating the database. So two CMDRS may be running around with entirely different data for the same system, and whoever lands and sells it first is the final form for the system in the database.
Might be worth testing.