Why do I get the feeling that the Z-rank room was the originally intended way to access the backroom content? The music really does fit the tone of "run down and shit" which makes sense for a room that requires getting the absolute worst rank possible.

And if you're going to hide shit that someone isn't likely to find on their first playthrough the best way to do it is by requiring getting a rank so low you have to be intentionally playing bad to get it.