Details 1: this could be how the backrooms work. if levels are near eachother, you can noclip onto another level.
Details 2: explanation to unescapable levels. if no levels are near enough, the noclipping process cannot be done.
Details 3: this could also explain levels which can noclip onto the frontrooms and nothing else. The Frontrooms is close to the level, so you can noclip to the frontrooms
Maybe I'm wrong? Say what I missed on the comments and say anything that I was right on.