To get on other paths you miss passwords usually and the X's mean a character is now dead. Also all paths are complete in this build. A is the true end of the game, the other paths are bad ends and such.
A public post on paths A,B,C,D-
https://www.patreon.com/posts/on-topic-of-42690779
Also the password is said by one of the characters on the day, The vault gives you a clue where to look when you go to enter it.