Generally speaking, most stuff in Psychopomp was created in the last year specifically for the game. However, there's still a good amount of things in there that existed before I even had the idea to create this game in particular.
Here's one example, the track that plays in upper floors of the first few levels, "Block Ambient" is actually an older music project I had laying around, taken and slowed down by a major percent. This is why Block Ambient is so long, a short 40 second loop has been stretched to a full six minutes, which is also why it doesn't appear on the OST.
This initial version is from 2020, and was most likely made for a DashBored update, but never got used.
Checking my project folder, I have about 1,977 music project files, the vast majority which are unused, and most which are like 5 seconds long. I usually make music right in the moment I need it, so the OST can be bespoke to the scene it plays in, however it can sometimes be fun to return to an old musical project and bring it into a project that people will actually see.