(spoiler maybe?) Does progress save across files?

[Radian]

Okay so. I've done a few different paths now (namely Stranger, Prisoner, and Gray I think? But after Prisoner was brought into... Uh. Amalgamation princess or whatever, I wanted to go back and see where the other choices lead. I tried a couple routes and one lead to act 3, gray (I think) where she floods the cabin.
I thought that was a bad ending but when I continued on it looked like that fragment also got unified with princess amalgamate.
I tried to go and get Prisoner on that file, but the game wouldn't let me go back to Prisoner's route through resisting the Narrator's hijacking my body.

So here's my question. Are routes I've finished did counted as 'completed' across all save files, especially since I got the steam achievement for it? Or would I need to achieve them all in a single save file?
And if it's the latter... ||Is there another way to get to Prisoner besides just trying to free her and getting possessed by the narrator?||

[Psyringe]

Finished routes only count for the current playthrough. They don't carry over to other playthroughs.

It is impossible to see all scenarios in one playthrough since there are more than 20 scenarios in the game, and you can only add a limited number of souls to the "entity" before the game comes to a conclusion. You cannot visit the same scenario twice in the same playthrough (there's an in-game explanation for that), and some are also mutually exclusive.

The game has very high replayability - many scenarios can also develop very differently depending on your decisions. If you would like to do some differently, don't worry - it's impossible to "ruin" a playthrough (but see below), and you can try again in the next one.

(The one possible way of "ruining" a playthrough is by accepting the so-called "good ending", since that ends the playthrough prematurely. But to get that ending, you have to show explicit disinterest in meeting further princesses, so I can't really blame the game for locking you out of that for the respective playthrough.)

[Radian]

Ah okay. I thought you had to see all the routes. Thank you!