It's a real thing. My first apartment was a scum pit and the landlord was just replacing our carpet when we moved in. It was this smelly stained high-pile squishy thing.
When the workers pulled the carpet up they were shocked to see another carpet under it. It was absolutely disgusting and the smell was horrid. But nothing could have prepared us for what came next...
When they pulled up that 2nd carpet there was a third! This was a perfectly preserved lime green football turf with a giant room-sized lemon yellow peace sign on it. This was in 1999, so that carpet had likely been sealed under the others for over 20 years at least.